TIP-1

                                   

If the value of something is increased by x % then decreased by y % then
resulting effect in percent : + x + y + xy/100

Example 1:

  The Salary of a worker is first increased by 10% and thereafter decreased by 5%. What is    the overall change in percent.

Solution:

overall change = + 10 - 5 + (+10)(-5)/100 = + 4.5 % (increased)

use (+) sign for increment and (-) sign for decrement.

Example 2:

A shopkeeper marks the price of goods 20% more than the real price. He allowed a discount of 10%.
What profit or loss did he get?
Solution:
Profit or loss the shopkeeper get: 20 - 10 + (+20)(-10)/100 = + 8% (profit)

Example 3:

The side of a square is increased by 30%. Find the percentage increase in area.

Solution:

Increase in area = 30 + 30 + (30)(30)/100 = 69%.

Example 4:

If the radius of a circle is decreased by 20%. What percent change in area?

Solution:

percent change in area: - 20 - 20 + (-20)(-20)/100 = -36% (decreased)

Example 5:

If the price of a shirt is increased by 15% than decreased by 15%. What is percent change?

Solution:

percent change : + 15 - 15 + (+15)(-15)/100 = - 2.25 % (decreased)

Example 6:

The length of a rectangle is increased by 40% and breadth is decreased by 40%. Find change in area.

Solution:

percent change in area: 40 - 40 + (-40)(+40)/100 = -16%(decreased)

Example:7

If a number is increased by 20% and again increased by 20%. By what percent should the number increased.

Solution:

percent increased: 20 + 20 + (+20)(+20)/100 = 44%(increased)