# A guide to attempting SI exam questions on arithmetic

Hyderabad: This article is in continuation to the last article on preparation for the Sub-Inspector of Police recruitment exams. Here are some subject-wise practice questions and answers along with explanations. Average 1. The average of ten numbers is 7. If each number is multiplied by 12, then the average of the new set of numbers […]

Published Date - 11:25 PM, Mon - 11 April 22

**Hyderabad:** This article is in continuation to the last article on preparation for the Sub-Inspector of Police recruitment exams. Here are some subject-wise practice questions and answers along with explanations.

**Average**

1. The average of ten numbers is 7. If each number is multiplied by 12, then the average of the new set of numbers is:

a) 7 b) 19 c) 82 d) 84 e) 96

2. Madhu has twice as much money as Suresh and Suresh has 50% more money than what Pavan has. If the average money with them is Rs110, then Madhu has

a) Rs 55 b)Rs 60 c)Rs 90 d)Rs 180 e)Rs 220

3. The average marks of 30 students in a class are 60. But a student marks is wrongly noted as 15 instead of 90. Find correct average marks?

a) 57.5 b) 58.5 c) 62.5 d) 63.5 e) 65

4. If a, b, c, d, e are five consecutive odd numbers, their average is:

a) 5(a d) b) 5(a b c d e) c)abcde d) a 4 e)None of these

5. The average weight of 3 men A, B and C is 84 kg. Another man D joins the group and the average now becomes 80 kg. If another man E, whose weight is 3 kg more than that of D, replaces A then the average weight of B, C, D and E becomes 79 kg. The weight of A is

a) 70 kg b) 72 kg c) 75 kg d) 80 kg e) 85 kg

6. The average weight of 9 mangoes increases by 20 gm if one of them weighing 120 gm is replaced by another. The weight of the new mango is

a) 180 gm b) 200 gm c) 260 gm d) 300 gm e) 360 gm

7. In seven given numbers, the average of first four numbers is 4 and that of the last four numbers is also 4. If the average of these seven numbers is 3, the fourth number is

a) 3 b) 4 c) 7 d) 11 e) 16

8. The average salary per month of 30 employees in a company is Rs 4000. If the manager’s salary is added, the average salary increases to Rs 4300, what is the salary of the manager

a) Rs 10,000 b)Rs 12,000 c)Rs 13,000

d) Rs 13,300 e)Rs 14,600

9. The average of 50 numbers is 38. If two numbers, namely 45 and 55 are discarded, the average of the remaining numbers is

a) 36.7 b) 37.5 c) 37 d) 38 e) 42

10. The average age of 40 students of a class is 15 years. When 10 new students are admitted, the average is increased by 0.2 years. The average age of new students is

a) 15.2 years b) 16 years c) 16.2 years d)16.4 years e)18 years

**KEY**

1. d

The average = 12 X 7 = 84

2. d

Let Pavan has Rs x

then Suresh has 150% of Rs x = = Rs

Madhu has 2 X = 3x

⇒ x 3x = 110 X 3

⇒ =330 ⇒ x= 60

Madhu has 3x = 3 X 60 = Rs 180

3. c

According to question total marks of 30 students = 30 X 60 = 1800

But the correct total marks of 30 students = 1800 – 15 90 = 1875

The correct average marks = = 62.5

**Short cut method**

The correct average marks = Given average (Correct marks – Wrong marks/ Number of students)

= 60 = 60 2.5 = 62.5

4. d

Clearly, b=a 2, c=a 4, d=a 6 and e=a 8.

Average = = (a 4)

5. c

A B C = (84×3) = 252kg,

A B C D=(80×4) = 320kg.

D = (320 – 252) = 68 , E = (68 3) =7l.

B C D E = (79×4)=316.

(A B C D) -(B C D E)=(320 – 316)kg = 4kg.

A – E = 4 = A = (4 E)=75kg.

6. d

Total weight increased (9 X 20) gm = 180 gm

Weight of new mango = (120 180) gm = 300gm

7. d

Fourth number=(4 X 4 4 X 4 – 7 X 3) = 11

8. d

Salary of the manager = (31 X 4300 – 30 X 4000) = Rs 13,300.

9. b

Total sum of 48 numbers = [50 X 38 – (45 55) ] = 1800

Required average = 1800 / 48 = 37.5

10. b

Sum of ages of 10 new students = (50 X 15.2 – 40 X 15) = 160 years

Average age of new students = 160/10 = 16 years

**To be continued…**

**Banda Ravipal Reddy**

**Director, SIGMA**

**Sai Institute of General Mental Ability**