Diffculty - Sub600
My method might seem long but once you get a hang of it, it seems easier.
Whenever we are asked to "increase" any quantity by some precentage value. Add that value with 100 and then perform the operations.
As in this case the sides are increased by 20%
By adding 20 to 100 we will get 120%
Both the sides are increased by 20% , therefore we have l=120% and b=120%
We have to find the area, formula for the area is l*b = 120%*120% = 14400 = 14400/100 = 144%
Remove the original 100 back to get 44%
Remember when we say 120 percent length, it means 100% of original length + 20% is the increament
You can use it with decimal too.
suppose l = x and b = y
Area = xy
New l2 = 1.2x (Why 1.2? becasuse original was 1x and it increased by 20% which is 0.2)
b2 = 1.2y
Area = 1.2x *1.2y = 1.44 xy