Practice questions for a better approach towards SI examinations

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 Average is just a mean value of all the given observations or we can say it is an arithmetic mean of observations. Average = […]

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
Average is just a mean value of all the given observations or we can say it is an arithmetic mean of observations.

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Average = Sum of observations / Number of observations
But, remember that this formula does not directly apply on average speed. Discussed in special cases.
To find average speed
Suppose a man covers a certain distance at x km/hr and covers an equal distance at y km/hr. The average speed during the whole distance covered will be 2XY/(X Y)
A motorist travels to a place 180 Km away at an average speed of 40Km/hr and returns 30 km/hr. His average speed for the whole journey in km/hr is?
36.28 b) 36.42 c) 34.82 d)34.28
Ans: d

Explanation:

Average speed
x=40 km/hr y=30 km/hr
Average speed

The mean weight of a group of seven boys is 56 kg. The individual weights (in kg) of six of them are 52, 57, 55, 60, 59 and 55. Find the weight of the seventh boy.

52 b)54 c)56 d)58

Ans: b
Explanation:
Total weight of 7 boys = (56 × 7) kg = 392 kg.

Total weight of 6 boys = (52 57 55 60 59 55) kg= 338 kg.

Weight of the 7th boy = (total weight of 7 boys) – (total weight of 6 boys)

= (392 – 338) kg= 54 kg.

The average score of a cricketer for ten matches is 38.9 runs. If the average for first six matches is 42, then average for last four matches is

a) 33.25 b) 32.25 c) 34.25 d) 34.50

Ans: c

Explanation:

The score of a cricketer for ten matches= 38.9×10=389
The score for first six matches= 42×6=252

The average for last four matches= (389 – 252)/4
= 137/4=34.25

The average of five consecutive odd numbers is 61. What is the difference between the highest and lowest numbers?
2 b) 5 c) 8 d) can’t be determined
Ans: c
Explanation:
Average of five consecutive odd numbers a, b, c, d, e= 61

(Note: The average of ‘n’ consecutive odd numbers is always a middle number, if ‘n’ is odd.)

i.e., middle number ‘c’ =61

Lowest number=a=61 – 4=57

Highest number=e=61 4=65

Difference between the highest and lowest numbers = 65 – 57 = 8

A cricketer has a certain average for 10 innings. In the eleventh inning, he scored 126 runs. Thereby increasing his average by 8 runs. His new average is?

56 b)52 c)46 d) 48

Ans: c

Explanation:

Let the average for 10 innings be X, then
10x 126=11x 88
X=38
New average = x 8 = 38 8 =46

The average of five numbers is 49. The average of the first and the second numbers is 48 and the average of the fourth and fifth numbers is 28. What is the third number?
92 b)91 c) 95 d) none of these
Ans: d
Explanation:
Sum of 5 numbers=49×5=245

Sum of first two numbers= 48×2=96
Sum of last two numbers= 28×2=56

Third number= 245 – (96 56) =245 – 152 = 93
The mean of 25 observations is 36. If the mean of the first 13 observations is 32 and that of the last 13 observations is 39, find the 13th observation.
23 b) 27 c)33 d)37
Ans: a

Explanation:

Sum of the first 13 observations = (32 × 13) = 416.
Sum of the last 13 observations = (39 × 13) = 507.
Sum of all the 25 observations = (36 × 25) = 900.
Therefore, the 13th observation = (416 507 – 900) = 23.
The average age of 30 students of a class is 14 years. When the age of the class teacher is included, the average increases 1 year. Find the age of class teacher?
a) 25 years b) 30 years c) 32 years d) 45 years
Ans: d
Explanation:
The total age of 30 students = 30 X 14 = 420 years

The total age of 31 persons = 31 X 15 = 465 years

Teachers age = 465 – 420 = 45 years

Short cut: Teacher’s age = No of students X increased average New average

= 30 X 1 15 = 45 years

In a school with 700 students, the average age of the boys is 13 years and that of the girls is 12 years. If the average age of the school is 12 years 9 months, then the number of girls in the school is?

200 b) 150 c) 125 d)175

Ans: d
Explanation:
Let total number of girls be =x

Then number of boys = 700 – x
Then

To be continued…
Banda Ravipal Reddy

Director, SIGMA
Sai Institute of General Mental Ability