Saturday, July 30, 2016

Solving the simultaneous equations 'Their' way - Part-2

Hello friends,

I am very happy that you liked my previous post on 'Solving Simultaneous Equation 'Their ' way" Thanks to many of you for explicitly expressing your interest and motivating me to continue with this sharing work.... 

To be honest, I was a bit reluctant to write the Part-2 now.... Why?

Because something more exciting has been happening in our class since past 2 days.... 
Yes, these government school students have surpassed my expectations, and I am so very happy that they keep jumping over the bar, whenever I raise it  for them !!

I will soon share that stuff too.... but first, lets complete the previous story :-)

For those, who have not yet read the Part-1 of this post, I would encourage you to do so, before you carry on ahead.... Here is the link to that story:

If you remember, they had made some interesting observations and had even used some sort of  'reasoning' before resorting to the trial and error method to find the solution....  I now wanted to see if it was possible to replace the trial and error element by the logical approach completely...

Both - Jeetu and Vaishnavi - were now working together.. I could see them struggling for the 'second' way... After allowing this struggle for some more time, I thought to intervene..... with a question....

"You have already figured out some relation between Square and Triangle (by comparing the first two figures)... Is it possible to go a little deeper?"

They listened to me with sincere attention but couldn't build upon it... 

May be my hint was not so clear... I stretched my hand further... 

"Can you figure out Triangle is bigger than Square by how much?"

Jeetu picked up !!

"Yes Sir...  It is bigger by 10. "

"Good... and how do you know this?"

And this time, I could see even Vaishnavi join him in the argument... It was a pleasure listening to them.

" If you add a square to circle, we get 10. But if we add a triangle to circle, we get 20.  This means, that extra 10 has come because of triangle."

"Ok.... And can we represent this using an equation?"

She wrote it this way:

"Ok... But what about that 10 you mentioned now?  How can you communicate about that?"

He borrowed the chalk from her and scribbled this immediately.

"Fantastic.... You have now got a new equation.....Can we use this along with the given data to solve the problem logically?"

They again seemed to be struck.... Please note that they were dealing with 'equations' for the first time.... And I was still expecting too much from them... Yes,.... too much !!  (why?)

I don't know what struck me... And I wrote a new problem besides this old one and drew their attention to this:

A + B = 50
A  - B = 18

"Looking at these two relations between the two numbers A and B, can you find out these numbers?"

Yes, this set of equations are very familiar to us (adults). We have probably studied those in our secondary school. But I would like to remind you that these students are just promoted to Class-6 and are from a municipal school. I had no idea what will unfold in next few minutes.. But one thing was sure, I trusted their instincts and abilities !! And I was also sure, that we will definitely learn something from this... 

Jeetu kept looking at these equations for a while......and......

"Sir... I got it."

"What?  You mean, you have got the two numbers? Beware! I am not going to accept your trial and error method this time."  

I tried to act smart and strict, but he continued with a confident smile.... Listen to him.....

"The two numbers differ by 18.... So first, we will remove this difference...... We will subtract this difference from their sum.....  i.e. 50 - 18 = 32......  Now since we have removed the difference between the two numbers, they have become equal... So each of the numbers is 32/2 = 16.....But both cannot be 16... as we know that they differ by 18..... So let us now add that difference to one number...... 16 + 18 = 34....... So the two numbers are 16 and 34."

What ?  Did you really get him ?? 

I am scared if your answer is Yes.... Because, I did not get this.... It seemed logical... a bit sensible.... but my logical brain hinted that there is something fishy.... Perfectly correct answer, but could not comprehend his logic immediately...

So I requested him to explain it to me again.... But he could not rephrase it in a different way.... Rather, he continued with much more confidence....  So I turned to Vaishnavi..

"Did you get what he said?"

"Yes sir... I understood.....!"

What??? This was now driving me crazy........ It was not that I did not trust his mathematical ability... In fact, Jeetu had surprised me many times before, but this time, somehow I was not sure about his logic.... I felt there is something that's got entangled...... and I am unable to see through it or unwind it......

There were two options before me now:  
1) stick with this new problem.... make him make me understand his method..... and/ or even arrive at the other method (which would make sense to me ;-)
2) accept his method for the time being & use this strategy to solve the original problem....

I chose the second option (why?) 

"Fine.... Now that you know how to solve such equations... Can you solve our original problem?"

They did not get what I meant... So I pointed at their new equation again....

"Did you see a similar equation in the previous problem?"

They pointed it out:  A - B = 18"

"What else did you require to solve this problem?"

No answer.....

"What would be the values of A and B, if I give you only this much information ---  about their difference?"

"They can have many answers then......"

"True... So why were you able to identify exactly one solution of A and B?"

"Because we had one more condition.......  A + B = 50"

"Hmmmm........ So now, are you getting where am I taking you?"

Vaishnavi screamed......

"Yes Sir.... I got it..... We have a similar addition condition in this problem also..."

Phew.................Finally !!!   :-)   :-)

She drew Jeetu's attention to Figure (iii)  -- the one that shows Triangle + Square = 24.

Jeetu looked up to me with wonder....  He was overwhelmed with the striking similarity..... I think he had also understood the reason I made them solve the new problem (of A, B)  :-)

He worked out the solution to the original problem in no time...... and got extremely delighted to see the same answer, that he had obtained some time back, using trial n error..

(I should have captured the joy on his face... I also forgot to take the snap of his written work....  I will do that on Monday and upload in the comments section of this blog)

But Vaishnavi took some time to understand this... Jeetu explained her.... Strangely, she was struggling to relate the A & B problem with this picture problem.....   He had used the same logic as before..... He was happy with this revelation...... And I was happy because he had finally got the taste of 'logical' approach...... However, there was something that was still bothering me..... I was not yet able to understand his method completely ;-(

I was going to look at it more closely after the class...... Meanwhile, other students grabbed me for some clarifications in the assignment problems..... But little did I know, that the game was not yet over.....

Vaishnavi came running to me, saying that she has figured out one more way....

"Oh really? Plz explain...."

I now decided to draw the attention of the whole class to this discussion.... I felt it was getting more interesting.... I gave them the background - what had happened till now.....  We three ensured that they understood what are we doing and why are we doing...... (some time was given to them too to think about the solution, but most of them resorted to Trial and Error methods..... Jeetu and Vaishnavi looked at me, with smile....  Probably, this reminded them of their journey :-)

So the setting was made.... Everyone was excited and curious now - to know one more logical approach, that was about to be unfolded by Vaishnavi........  

And I am sure, even you too are curious  :)

So here it is.. This is what she scribbled on the board, with her voice-over in the background...  

And this just blew me away !! She had hit a Sixer !!

Take a careful look at her diagram... how beautifully she has merged the three figures in the problem into just two figures....

I would suggest you to analyze her work before reading further....


What she said (while drawing) was:

" If we add first two diagrams of the problem, then we get a total of 4 shapes with their value = 30 (20+10).... Now we remove Square and Triangle from this combined set.....(and while saying this, she draws a box around the two lower figures, if you can see.....the Pictorial subtraction! ) ...... We are left with only two Circles now....  Further, we know the total value of Square + Triangle.... Its 24... So removing this pair from the complete set means subtracting 24 from 30..... Hence Two Circles = 6..... So one circle = 3..... Now, we can easily figure out that Square = 7 and Triangle = 17.... So the required total of all three is 3+7+17 = 27..... " 

Now, isn't that just beautiful ??

Probably, you will appreciate this much more if you consider -
a) the way we are taught /  have solved such problems (dry way)
b) the age and background of this child.

I was still having conversation with Vaishnavi as to what made her think of this approach.... and she was trying to explain me....... and meanwhile, I heard another voice ---

"Sir, even I got another way !!"

This was from Payal....  I was so happy to hear from her after long time.... 

"Yes, Payal.... Plz explain to the class..."

"No sir.... I am not sure..... You plz check first....."

"Its ok... We all will try to understand it together...."

But she insisted that I should verify it first, before its discussed with the class... I agreed. And I was about to read her work, she intervened....

"Sir, I don't know the reason.....Why it works.... I have just guessed this method..... I don't know if its correct...."

"Its ok.... Let me see...."

Her work was a bit messy, so I requested her to explain.... This is what she had done:

" Half of 10 is 5 (pointing at the figure (i) of the problem)
  Half of 20 is 10 (from the fig (ii))
  Half of 24 is 12 (from fig (iii)
  If we add 5 + 10 + 12, we get 27... Its the correct answer."

And I was like....... Again, bowled !!

Did you understand this ??

I did not (at that instant).... So  I asked Payal for the reason.... And she argued --

"Sir, I told you... don''t ask me the reason.... I have simply guessed the method..... "

So I thought to share this with the whole class.... and while explaining her method to the class, something struck me ----  I started thinking while explaining... 

Can you ponder over this for a while, before reading ahead..... as to why this works? what could be the logic behind this method that makes it work? 


"Payal has done half of the value in the fig (i)...  10/2 = 5... But what does this 5 signify? How can we interpret this operation?"

Sahil responded: " Sir, it means Half Circle + Half Square = 5"


"Then she has halved the value in fig (ii) ... 20/2 = 10..... Means?"

Many voices join this time:   " Half Circle + Half Triangle = 10"

"And how does her last operation get interpreted?" 

" It means Half Square + Half Triangle = 12"

I had got it half the way, what's happening..... and I was so very delighted to dawn upon this beautiful approach... But I chose to stay silent and ask the students now  --

"So why does adding these three numbers give us the required solution?"

Silence for about 25-30 seconds.....and ......... Vaishanvi erupts  :-)

"Sir, I understood why it works..... Shall I explain? "

All heads turn around, looking towards her with surprise...My god, the girl is on hat-trick! :-)

I ask Payal if she has been able to figure out the reason...She gives me a shy look and a hiding smile.... I probe her....

"Sir, let Vaishnavi explain.... I told you, I don't know the reason....."

I could see students relishing this humorous moment :-)  :-)

The Girl takes the charge again... and scribbles up with the same style...

i) She first draws the two halves - of square and of circle, and equals it to 5.....  (equation (i))
ii) then she draws half of triangle, completes the circle, and writes 10 .... (eq. (ii))
iii) finally she completes the triangle and even square, and writes 12...... (eq. (iii))
iv) then she adds up this 12, 5 and 10 to get 27.... (she has erased 12 and has written 27 at its place)

So how was it ??    :-)   :-)

In case you feel that the story ends here, then yo are grossly mistaken..... 

We explored some more 'logical' methods to solve this problem..... 
What?  Some more?  

Yes.... But I am not going to share those in this post now.......  May be in Part-3   :-)

Till then, how about YOU thinking out some more approaches?   You can discuss these with your children/ students and let me know....  I would love to know some from you.....  

Let me give you some hint....... for some more approaches....

Yes, the hint is There in the above post ... Lets see if you can get it :)

Happy Mathing !! 

Rupesh Gesota


  1. I worked Payal's answer as follows... If you add all three pictures, you have two circles, two triangles and two squares. So the fourth picture which asks for one circle, one triangle, and one square is exactly half of the sum of all the other three pictures. Only problem is that we don't really find out the breakup of each symbol's weight in this way! :)

  2. On Sun, Jul 31, 2016 at 6:14 AM, Tara Kini wrote:
    Just totally amazing, Rupesh. Firstly , your patience with the learners to let them think solutions through, your excitement over their journey and your understanding of their process!!

    All these result in their ability to think through it all themselves. These children will be fabulous in every other area too! What a temple of learning you have created!


  3. I'm spellbound. Once again, these children have surpassed expectations. I love this approach that you have adopted,making Math so much more fun to learn. Hats off to these children and to you too, Rupesh. I will definitely share this with my kids.


  4. On Mon, Aug 1, 2016 at 8:52 PM, Geeta Suresh wrote:

    Hi Rupesh,

    Thanks a lot for such an enlightenment. Most of the time the teacher gets to learn more from children than what teacher can give it to them. The sad part is not every teacher is like you. I am reading a book by J Krisnamurty "A flame of Lerning" He speaks of what teachers can do when teaching. If possible read it.

    As for the posting the Jeetu method will also work:

    A + B = 50
    A - B = 18

    ( A + B) - (A - B) = 50 - 18
    2B = 32
    B = 16

    But I liked the last solution given by Payal and the beautiful explanation given by Vaishnavi. Hats off to you and all the kids.
    I did have very good maths teachers, but I wish they were more like you.

    Thanks again.
    Best Regards,