percentage change question

1}A quantity is increased vy 10% and then decreased by 15%..
find the percentage change..
Let x be the original quantity
Then the new quantity
= x(1+ 10%)(1- 15%)
= 0.935x

percentage change
= 100%(x-0.935x)/x
= 6.5%

2)the area of a park is at first increased by 20% and then increased by 15% to become 14145m square. what is the original area of the park?

Let x m^2 be the original area of the park
x(1+20%)(1+15%) = 14145
x(1.2)(1.15) = 14145
1.38x = 14145
x= 10250

The original area of the park is 10250m^2

3)the rent of a flat is increased from $7200 by 15%and then decreased to $7038 by x%.find x.

7200(1+15%)(1-x%) =7038
1.15(1-x%) = 0.9775
1-x% = 0.85
-x% = -0.15
x = 15

4)jacky's monthly salary is 8300.if his monthly salary is increasd by 20% and then increased by 25% find the overfall percentage change of his monthly salary when compared with his original monthly salary.

New salary
= $8300(1+ 20%)(1+25%)
= $12450

overfall percentage change of his monthly salary
= 100%(12450-8300)/8300
= 50%

His monthly salary is increased by 50%.

Ans1: 100%-[1(100%+10%) x (100%-15%)]=6.5%

Ans2:(14145/115%)/120%=10250M sq.

Ans3:100%-[7038/(7200x115%)x100%]=100%-[(7038/8280)x100%] =100%-85%=15% so x=15

Ans4:[(8300x120%x125%)-8300]/8300x100%=50%
or 120%x 125% -100%=50%