PERCENTAGE INCREASE AND DECREASE PRACTICE QUESTIONS

Question 1 :

Increase $5000 by 20%

Question 2 :

Decrease $85 by 22%

Question 3 :

Increase 78 kg by 3%

Question 4 :

Increase 800 m by 15%

Question 5 :

What is the overall effect of increasing $100 by 10% and then decreasing the result by 10%? 

Question 6 :

When decreasing a quantity by 10% in two successive years, the overall result is to decrease the original by 19%.

Question 7 :

Find the overall effect of increasing a quantity by 20% each year for 3 successive years.

Question 8 :

Increase 150 by 10% and decrease the same by 15%. Find the new number in each case.

Question 9 :

At the beginning of the month of January, a stock is worth d dollars per share. The value of the stock  increases 5 percent per month for each of the first two months and 25 percent for the third month. During the
fourth month, the value, per share, decreases by 20 percent. In terms of d, what is the value of the stock, per share, at the end of the fourth month?

(A) 0.98725d     (B) 0.99225d    (C) 1.1025d    (D) 1.135d

(E) 1.15d

Question 10 :

In 2008, Zinah earned 14% more than in 2007, and in 2009 Zinah earned 4% more than in 2008. If Zinah earned y times as much in 2009 as in 2007, what is
the value of y ? 

A) 0.5600     B) 1.0056    C) 1.1800      D) 1.1856

Question 11 :

The amount of Hanna’s bill for a food order was $50. Hanna gave a tip of 20% of the amount of the bill. What is the amount, in dollars, of the tip Hanna gave?

Question 12 :

A high school basketball team won exactly 65 percent of the games it played during last season. Which of the following could be the total number of games the team played last season?

A) 22    B) 20   C) 18      D) 14

Question 13 :

The table above presents information about the 810 train cars in service on a railroad. Approximately what percentage of the train cars in service are double-decker cars that have been in service for less than 10 years?

A) 2 percent   B) 7 percent  C) 10 percent   D) 16 percent

(1)  Solution :

100%  =  5000

Increase by 20%  ==>  120% of 5000

=  1.20(5000)

=  6000

(2)  Solution :

100%  =  85

Decrease by 22% :

100-22  ==>  78

=  78% of 85

=  0.78 (85)

=  66.3

(3)  Solution :

100%  =  78 kg

Increase by 3% :

100+3  ==>  103

=  103% of 78

=  1.03(78)

=  80.34

(4)  Solution :

100%  =  800

Increase by 15% :

100+15  ==>  115

=  115% of 800

=  1.15(800)

=  920

(5)  Solution :

100%  =  100

Increase by 10% :

100+10  ==>  110

=  110% of 100

=  1.10(100)

=  110

Now 100%  =  110

Decrease by 10% :

100-10  ==>  90

=  90% of 100

=  90

(6)  Solution :

Let the original quantity be 100.

Decrease the quantity by 10% means 90% of 100.

In the first year, after the first decrease the original quantity becomes 90.

100%  =  90

Decrease of 10% :

100 - 10  ==>  90%

So 90% of 90  =  0.90(90)

Overall result  =  81

Decrease of 19% from the original :

100 - 19  ==>  81%

So, 81% of 100  =  81

In both ways, we get the same answer.

(7)  Solution :

Let 100 be the original quantity.

Increase of 20% :

100 + 20  ==>  120% of original 

After 1 year  =  120

In the second year  =  120% of 120

=  144

In the third year  =  120% of 144

=  172.8

So, effect of increasing is 72.8%.

(8)  Solution :

100%  =  150

110% of 150  =  1.10(150)

=  165

After 10% of increment the new number is 165.

Now, 100%  =  165

100-15  ==>  85%

=  85% of 165

=  0.85(165)

=  140.25

After 15% of decrement the new number is 140.25.

(9)  Solution :

Worth of each share = d

Worth of share after the first month = 105% of d

Worth of share after the second month

= 105% of (105% of d)

Worth of share after the third month

= 125% of 105% of (105% of d)

Worth of share after the fourth month

= 80% of 125% of 105% of (105% of d)

= 0.80 x 1.25 x 1.05 x 1.05d

= 1.1025d

So, option C is correct.

(10) Solution :

Let x be Zinah's earning in 2007

Zinah's earning in 2008 = 114% of x

Zinah's earning in 2009 = 104% of 114% of x

= 1.04(1.14x)

= 1.1856x

So, option D is correct.

(11) Solution :

Amount paid for food = $50

He is paying a tip of 20%

Amount paid by Hanna after the tip = 120% of 50

= 1.20(50)

= 60

(12) Solution :

Let x be the total number of games they played

Number of games they won = 65% of x

= (65/100) x

= (13/20) x

So, total number of games should be 20, option B is correct.

(13) Solution :

Required percentage = [ 16 / (16 + 82) ] x 100%

= (16/98) x 100%

= 0.1632 x 100%

= 16.3%

Approximately 16%, option D is correct.

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