# Diligent practice of arithmetic questions helps you crack SI exam

By Banda Ravipal Reddy 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 mean of the 40 observations was 24. It was found later that an observation 38 was wrongly taken […]

Published Date - 11:15 PM, Fri - 15 April 22

**By** Banda Ravipal Reddy

**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 mean of the 40 observations was 24. It was found later that an observation 38 was wrongly taken as 14. The corrected new mean is?

a) 23.2 b) 24.1 c) 24.6 d)28.1

**Ans: c**

**Explanation: **

Sum of 40 observations

Actual sum = 960 38-14 = 984

Correct average

2. The average expenditure of 9 friends out of 10 is Rs 20. The tenth friend’s expenditure is Rs 45 more than the average expenditure of all 10 friends. Find the total expenditure of all 10 friends?

a) Rs 245 b) Rs 250 c) Rs 255 d) 260

**Ans: b**

**Explanation: **

Let average expenditure of 10 friends = x

Tenth friend expenditure = x 45

Total expenditure of ten friends= 10x = (9 × 20) x 45

9x = 225

x = 25

Total expenditure of ten friends= 10x = 10 × 25 = Rs 250

3. Average weight of 20 people increased by 1.5 kg when one person of 50 kg is replaced by a new man. Then find the weight of the new man?

a) 51 kg b) 60 kg c) 70 kg d) 80 kg

**Ans: d**

**Explanation: **

Total increased weight = 20 × 1.5 = 30 kg

Weight of new person = 50 30 = 80 kg

4. The average weight of A and B is 50 kg; B and C is 70 kg and C and A is 60 kg. Then find the weight of B

a) 40 kg b) 55 kg c) 58 kg d) 60 kg

**Ans: d**

**Explanation: **

The total weight of A and B = 2 × 50 = 100 kg

The total weight of B and C = 2 × 70 = 140 kg

The total weight of C and A = 2 × 60 = 120 kg

2(A B C) = 80 120 160 = 360

A B C = 180 kg

B’s weight = 180 – 120 = 60kg

5. The average monthly income of P and Q is Rs 5050. The average monthly income of Q and R is Rs 4250 and the average monthly income of P and R is Rs 3200. The monthly income of P is?

a) 3500 b) 4000 c) 4050 d) 4500

**Ans: b**

**Explanation: **

Total salary of P and Q

Total salary of the Q R

Total salary of the P R

By adding we get 2 (P Q R) =25000

P Q R = 12500

P 8500= 12500

P=4000

6.A library has an average of 321 visitors on Sundays and 180 on other days. The average number of visitors per day in a month of 30 days beginning with a Sunday?

a) 201 b) 205.3 c) 203 d) 203.5

**Ans: d**

**Explanation:**

The month begins with a Sunday, so there will be 5 Sundays in the month.

Required average

7. The average marks of 30 students in a class are 60. But a student’s marks are wrongly noted as 15 instead of 90. Find correct average marks.

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

**Ans: c**

**Explanation:**

According to question, total marks of 30 students = 30 × 60 = 1800

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

The correct average marks = 1875/30 = 62.5

**Short cut method:**

The correct average marks = Given average (Correct marks – Wrong marks/ Number of students) = 60 ( ) = 60 2.5 = 62.5

8. Five years ago, the average age of a family of 4 members was 23 years there. Including a baby, the average age is still the same today. What is the age of the baby now?

a) 2 years b) 3 years c) 4 years d) 1 year

**Ans: b**

**Explanation: **

Total age of the four members 5 years ago= 4×23=92

Total age of 4 members now = 92 (4×5)=112

Total age of 5 members now = 23×5=115

Age of baby = 115-112=3 years

9. A, B, C and D are four consecutive number. If the sum of A and D is 103 what is the product of B and C?

a) 2652 b) 2562 c) 2970 d) 2550

**Ans: a**

**Explanation: **

Average of A and D=

Average of A and D = average of 4 numbers

The numbers are

50, 51, 52, 53

B=51 C=52

B×C=51×52=2652

10. The average of 50 numbers is 30. If two numbers, 35 and 40, are discarded, then the average of the remaining numbers is nearly:

(a) 30 (b) 28.68 (c) 29.68 (d) 30.68

**Ans: C**

**Explanation: **

Total sum of 48 numbers = (50 × 30) – (35 40)

= 1500 – 75= 1425

Average = 1425/48

= 29.68

To be continued…

**Director, SIGMA**

**Sai Institute of General Mental Ability**

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