Aptitude : Percentage

(11) A number is increased by 20% and then decreased by 20%. What is the net change?

• (a)20 Percentage
• (b)25 Percentage
• (c)4 Percentage
• (d)6 Percentage

Answer

Correct Answer : (c) 4 Percentage
Let’s say the original number is 100. If we increase it by 20%, we get 100 * 1.2 = 120. If we then decrease 120 by 20%, we get 120 * 0.8 = 96.
So, the final number is 96, which is 4% less than the original number of 100.
This can be explained mathematically by using the following formula:
Net change = (original value * (1 + increase%) * (1 – decrease%))
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In this case, the original value is 100, the increase is 20%, and the decrease is 20%. Plugging these values into the formula, we get:
Net change = (100 * (1 + 0.2) * (1 – 0.2)) = 96
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Therefore, the net change is a decrease of 4%.

(12) The population of a town increases by 5% annually. If its present population is 20000, what will be its population after 2 years?

• (a)22100
• (b)22150
• (c)22500
• (d)22050

Answer

Correct Answer : (d) 22050
If the population increases annually by 5%, it becomes 1.05 times its size each year.
So, after 2 years, the population will be 20000 * (1.05^2)
=22050.

(13) If 30% of (50% of a number) is 60, then what is the number?

• (a)600
• (b)400
• (c)500
• (d)450

Answer

Correct Answer : (b) 400
Let’s assume the number is x.
Then 30% of (50% of x) = 60 implies 0.3 * 0.5 * x = 60.
Solving this we get x = 400.

(14) The price of a commodity is cut by 20%. To restore it to the original price, it must be increased by what percent?

• (a)25 Percentage
• (b)30 Percentage
• (c)35 Percentage
• (d)40 Percentage

Answer

Correct Answer : (a) 25 Percentage
Original price = 100
New price = 80
Increase = 100 – 80 = 20
Percentage increase = 20 / 80 * 100 = 25%

(15) A student scored 80% marks in five subjects together: Science, Mathematics, English, Social Science and Hindi. Each subject carries 100 marks. How many marks did he score in English if his marks in English are 90% of marks in Science?

• (a)80
• (b)72
• (c)90
• (d)75

Answer

Correct Answer : (b) 72
The student scored 80% marks in five subjects together, which means he scored 80% of 500 marks, or 400 marks. Since each subject carries 100 marks, he scored 400 / 5 = 80 marks in each subject.
However, we are told that his marks in English are 90% of marks in Science. This means that he scored 90% of 80 marks, or 72 marks in English.
Therefore, the student scored 72 marks in English.