Let us take a look at a grade 3 problem:
Find the perimeter of a rectangle whose length is 2 m and breadth is 10 cm.
Most of the children are unaware of the significance of units, hence, they might simply ignore the units and attempt it this way :
2 + 10 + 2 + 10
I want them to understand the difference between
2 + 10 + 2 + 10 & 2 m + 10 cm + 2 cm + 10 cm
If I say, you need to have the same units for addition/subtraction, children might simply follow because ‘teacher is saying so’. Conversion of units and its importance is quite an abstract concept for 8 – 9 year old children. They need a concrete example to understand and visualise this concept of same vs. different units.
Digits have no definite value without units. Units are the game changers in Maths.
Consider these digit-unit pairs :
10 Km, 10 gm, 10 Secs, 10 litres
All of them have the digit 10 but are they all the same ? Units are making them all different. Do you agree ?
I want children to ‘see’ this concept that it is the “unit” that decides the exact value of a digit.
Let me share the approach that I use in my classroom to explain this abstract concept :
Me: If I give you $100 & Rs. 100, how much money would you have in total ? ( Rs is Indian currency )
Student : (Thinking … ) $100 & Rs. 100
Me : Very smart answer 🙂 What’s the total amount ?
Student : (Screaming silence)
Me : Can you say that you have $ 200 in total ?
Student : No.
Me : Can you say that you have Rs. 200 in total ?
Student : No.
Me : What do you understand from this example ?
Student : Hmm…., I cannot add $100 & Rs. 100. ( This is the Aha… moment for any student who is struggling with units)
Me: Right. What do you need to do so that you can add them ?
Student : I need to convert Rs. 100 to dollars. ( Rs. 100 = $2 assuming 1 Dollar = 50 Rs. )
Me : Can we do it the other way also ? Can we convert $100 to Rs. ?
Student : Yes, that’s also possible. $100 = 50 X100 = Rs. 5000. So, total amount is Rs.5100 .
I have tried this method with multiple students and after this conversation, all of them have got a crystal clear understanding about the significance of units. Now, they don’t just mechanically convert units to make them same. Rather, they understand the reasoning behind it.
I would encourage you to discuss this with your children/ students and let me know if it gives them a clearer perspective of units. Your feedback would surely help me in this journey of Making Maths Simple & Visual.