Master in arithmetic problems for SI exams

By M.Venkat This article is in continuation to the last article on arithmetic that will aid you in your preparation for government recruitment exams. Here are some practice questions along with solutions on the Average topic. 1. In a school, the average age of students is 6 years and the average age of 12 teachers […]

By M.Venkat

This article is in continuation to the last article on arithmetic that will aid you in your preparation for government recruitment exams. Here are some practice questions along with solutions on the Average topic.

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1. In a school, the average age of students is 6 years and the average age of 12 teachers is 40 years. If the average age of the combined group of all the teachers and students is 7 years, then the numbers of students is?

a) 496 b) 396 c) 596 d) 555

Ans: b

Solution: S T
6 40
7
33 1
33 : 1
1 ->; 12
33 ->; 33 × 12 = 396

2. A class of 60 students contributed Rs 4800 for a charity. If each boy has contributed Rs 94 and each girl contributed Rs 73, find the number of girls in the class.

a) 20 b) 40 c) 30 d) 25
Ans: b

Solution: B G
94 73
80
7 14
4800/60 = 80
1 : 2
3 ->; 60
2 ->; 20 × 2 = 40

3) The average mathematics marks of two sections A and B of Class IX in the annual examination is 74. The average marks of section A are 77.5 and that of section B is 70. The ratio of the number of students of section A and B is?
a) 8:7 b) 7 : 8 c) 5 : 7 d) 7 : 5

Ans: a

Solution: A B
77.5 70
74
4 3.5
4 : 3.5

8 : 7

4. Of the four numbers, the first number is twice of the second, the second is one-third of the third, and the third is 5 times of the fourth. The average of the number is 24.75. The largest of these numbers is?

a) 9 b) 45 c) 55 d) 30

Ans: b
Solution: a = 2b, b = 1/3 c, c = 5d
a : b = 2 : 1 } a : b : c = 2 : 1 : 3}

b : c = 1 : 3 c : d = 5 : 1
a : b : c : d = 10 : 5 : 15 : 3
33 parts ->; 24.75 × 4
15 parts ->; ?
(24.75 × 4 × 15)/33 = 45

5) In a family of 8 adults and some minors, the average consumption of rice per head per month is 10.8kg. While the average consumption for adults is 15 kg per head and for minors it is 6kg per head. The number of minors in the family is?

a) 6 b) 7 c) 8 d) 9

Ans: b

Solution: Adults (15) minors(6)
10.8

4.8 4.2

= 8 : 7

8 ->; 8

7 ->; ? = 7

6. The average of the test scores of “m” students is 70 and that of “n” students is 91. When the scores of both the classes are combined, the average is 80. What is n/m?

a) 10/13 b) 10/11 c) 11/10 d) 13/10

Ans: b

Solutions: m n
70 91
80
11 10
n/m = 10/11

7. The average of three numbers is 135. The largest number is 195 and the difference between the other two is 20. The smallest number is?

a) 65 b) 95 c) 105 d) 115

Ans: b

Solution: a b c = 3 × 135

Let ‘c’ be the largest number

a b = 405 – 195

a b = 210

a – b = 20

2a = 230 =>; a = 115, b = 95

b = 95.

To be continued..

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