Q. 18

The length of a rectangle is increased by 15% and the breadth is reduced by 15%. Let’s work out in percentage the increase or decrease of area.

Answer :

Given: The percentage increment of the length of the rectangle=15%

The percentage decrement of the breadth of the rectangle=15%

Tip: if y is increased by x% then the new value of y is

: if y is decreased by x%, then the new value of y is

Let the length of the rectangle be “L” units.

Let the breadth of the rectangle be B units

Therefore, initially before any change in the lengths of both the length and breadth of the rectangle is


Now, Using tip (i)

The new length of the rectangle will be:

=L units =L units

Now, Using tip (ii)

The new breadth of the rectangle will be:

=B units. =B units

Therefore, the new area of the rectangle will be:



Therefore, the decrement in area= LB- LB


Therefore, percentage decrement in area,




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West Bengal - Mathematics