Numbers

Question 1

Which is not the prime number?

• A. 43
• B. 57
• C. 73
• D. 101

Answer: (B)

Arithmetic Aptitude Numbers
Discuss it

A positive natural number is called prime number if nothing divides it except the number itself and 1. 57 is not a prime number as it is divisible by 3 and 19.

Question 2

How many terms are there in 3,9,27,81........531441?

• A. 25
• B. 12
• C. 13
• D. 14

Answer: (B)

Arithmetic Aptitude 4 Numbers 50 Aptitude & Reasoning MCQs with Answers
Discuss it

3, 9, 27, 81..............531441 form a G.P. 
with a = 3 and r = 9/3 = 3
Let the number of terms be n

According to the formula, N^th term of the G.P is represented as T_n = a x r^n-1

Then 3 x 3n-1 = 531441
∴ 3n = 312
∴ n = 12

Question 3

If the average of four consecutive odd numbers is 16, find the smallest of these numbers?

• A. 5
• B. 7
• C. 13
• D. 11

Answer: (C)

Arithmetic Aptitude 4 Numbers 50 Aptitude & Reasoning MCQs with Answers
Discuss it

Let the numbers be x, x+2, x+4 and x+6
Then (x + x + 2 + x + 4 + x + 6)/4  = 16
∴ 4x + 12 = 64
∴ x = 13

Question 4

If the sum of two numbers is 13 and the sum of their square is 85. Find the numbers?

• A. 6 & 7
• B. 5 & 8
• C. 4 & 9
• D. 3 & 10

Answer: (A)

Arithmetic Aptitude 4 Numbers 50 Aptitude & Reasoning MCQs with Answers
Discuss it

Let the numbers be x and 13-x Then x² + (13 – x)² = 85 ∴ x² + 169 + x² – 26x = 85 ∴ 2 x² – 26x + 84 = 0 ∴ x² – 13x + 42 = 0 ∴ (x-6)(x-7)=0 Hence numbers are 6 & 7

Question 5

The difference between a two-digit number and the number obtained by interchanging the positions of its digits is 36. What is the difference between the two digits of that number?

• A. 4
• B. 5
• C. 6
• D. None of these

Answer: (A)

Arithmetic Aptitude 5 Numbers
Discuss it

Let the ten’s digit be x and unit’s digit be y
Then (10x + y) – (10y + x) = 45
         9(x – y) = 36
           x – y = 4

Question 6

A two-digit number is such that the product of the digits is 12. When 9 is subtracted from the number, the digits are reversed. The number is:

• A. 34
• B. 62
• C. 43
• D. 26

Answer: (C)

Arithmetic Aptitude 5 Numbers 50 Aptitude & Reasoning MCQs with Answers
Discuss it

Let the tens digit of the number be a and ones digit be b.

Given:
ab = 12 ................(i) and,
(10a + b) - (10b + a) = 9
10a + b - 10b - a = 9
9a - 9b = 9
9(a-b) = 9
(a-b) = 1 .................(ii)

Factors of 12 = 1, 2, 3, 4, 6, 12. and from equation (ii), (a - b) = 1 So, a = 4 & b = 3. Required number = ab = 43.

Question 7

Find a positive number which when increased by 16 is equal to 80 times the reciprocal of the number

• A. 20
• B. -4
• C. -10
• D. 4

Answer: (D)

Arithmetic Aptitude 5 Numbers 50 Aptitude & Reasoning MCQs with Answers
Discuss it

Let the number be x.
Then x + 16 = 80 * (1/x)
x2 + 16x – 80 = 0
x2 + 20x – 4x – 80 =0
(x + 20) (x -4)
Therefore x = 4

Question 8

What is the sum of two consecutive odd numbers, the difference of whose squares is 56?

• A. 30
• B. 28
• C. 34
• D. 32

Answer: (B)

Arithmetic Aptitude 5 Numbers 50 Aptitude & Reasoning MCQs with Answers
Discuss it

Let the no. be x and (x +2).
Then (x + 2)2 – x2 = 56
4x + 4 = 56
x + 1 = 14
x = 13
Sum of numbers = x + (x +2) = 28

Question 9

The product of two numbers is 108 and the sum of their squares is 225. The difference of the number is:

• A. 5
• B. 4
• C. 3
• D. None of these

Answer: (C)

Arithmetic Aptitude 5 Numbers 50 Aptitude & Reasoning MCQs with Answers
Discuss it

Let the numbers be x and y.
Then xy = 108 and x2 + y2 = 225
(x –y)2 = x2 + y2 – 2xy
(x –y)2 = 225 – 216
(x –y)2 = 9
Therefore (x –y) = 3

Question 10

The average of 21 results is 20. Average of 1^st 10 of them is 24 that of last 10 is 14. the result of 11'th is :

• A. 42
• B. 44
• C. 46
• D. 40

Answer: (D)

Arithmetic Aptitude 6 Numbers 50 Aptitude & Reasoning MCQs with Answers
Discuss it

 11'th result = sum of 21 results – sum of 20 results
             = 21 x 20 – (24 x 10 + 14 x 10)
             = 420 – (240 + 140)
             = 420- 380 = 40