TNPSC - Mathematics Model Questions and Explanations

1.  A printer numbers the pages of a book starting with 1 and uses 3189 digits in all. How many pages does the book have ?

a. 1000

b. 1074

c. 1075

d. 1080

Answer: 1074

Explanation

No.of digits in 1-digit Page nos. = 1x9 = 9.

No.of digits in 2-digit Page nos. = 2x90 = 180.

No.of digits in 3-digit Page nos. = 3x900 = 2700.

No.of digits in 4-digit Page nos. = 3189-(9+180+2700) = 3189-2889 = 300.

Therefore No. of pages with 4-digit page nos. = (300/4) = 75.

Hence, total number of pages = (999+75) = 1074.

2. The total of the ages of Kumar, Murugan and Manikandan is 90 years. What was the total of their ages 3 years ago ?

a. 79 years

b. 80 years

c. 81 years

d. 87 years

Answer: 81 years

Explanation = (90-3x3) years = (90 - 9) years = 81 years.

3. 12 year old Selvam is three times as old as his brother Rajkumar. How old will Selvam be when he is twice as old as Rajkumar ?

a. 14 years

b. 16 years

c. 18 years

d. 20 years

Answer: 16 years

Explanation: Selvam present age = 12 years, Rajkumar present age = 4 years.

Let Selvam be twice as old as Rajkumar after x years from now.

Then, 12 + x = 2 (4 + x)  12 + x = 8 + 2x  x = 4.

Hence, Selvam required age = 12 + x = 16 years.

4. A motorist knows four different routes from Bristol to Birmingham. From Birmingham to Sheffield he knows three different routes and from Sheffield to Carlisle he knows two different routes. How many routes does he know from Bristol to Carlisle ?

a. 04

b. 08

c. 12

d. 24

Answer: 24

Explanation: Total number of routes from Bristol to Carlisle = (4 x 3 x 2) = 24.

5. What number should come next at this series: 8, 10, 9, 11, 10, 12, ... 
a. 12
b. 11 
c. 10
d. 09 


Answer: 11