I realise that many of my Sec 2 students find proportion question pretty easy except questions on the type of questions where by1 variable is changed and the question ask how will the other variable be affected.
Hence, I am going to list down the 3 steps method taught during my lessons.
Qns) Given that x is directly proportional to y2(square) and that x=17 for a certain value of y. When y doubles in value, what is the value of x?
FIRST STEP: WRITE THE MAIN EQUATION
x=ky2 , k is a constant ————-> Equation 1
Input any details from the question
17= k(y square)
SECOND STEP: MAKE K THE SUBJECT
k = 17/y square ———————–> Equation 2
THIRD STEP: EXPRESS NEW Y IN TERMS OF ORIGINAL Y
y(new) = 2y ———————-> Equation 3
LASTLY SUB EQUATION 3 and 2 IN EQUATION 1
x (new) = 17 /y square times ( 2y ) square
= 17 / y square times 4 y square
= 17 times 4 ( The y square got camcelled off)
These 3 steps method can be used always for this type of questions. So the key is consistency!
I am going to do another similar question on inverse proportion via youtude video in my next post. 🙂
Im expecting my sec 2 kids to excel in this type of questions soon. 🙂