WBCS Practice Set 6 on Arithmetic with Answers

Submitted by Atanu Chaudhuri on Sat, 16/06/2018 - 16:22

$WBCS Practice Set 6 on Arithmetic with Answers$

6th selected WBCS math question set for Arithmetic practice

Solve 10 questions in WBCS practice set 6 on arithmetic in 10 minutes. Verify results from answers. Solve the questions by basic concepts and techniques.

Questions are on ratio, number system, mixture, series, pipes cisterns, fractions, train running, boats rivers.

It should be useful for prelims of other competitive exams also.

The solution set (linked at the end) explains how to solve the questions quickly in mind.

Answers to the questions are at the end.

WBCS practice set 6 on Arithmetic questions: time to answer 10 mins

Problem 1

If the ratio of three numbers are $3:4:5$ and their LCM is 1200, then the smallest number is,

Problem 2

The least number which when diminished by 5 is divisible by each of 21, 28, 36, 45 is,

425
1260
1265
1259

Problem 3

A container contains $x$ litres of milk. $y$ litres of milk was taken out and replaced by water. How much milk will be there in the container after carrying out this process $(n-1)$ times?

$x\left(1-\displaystyle\frac{y}{x}\right)^n$ litres
$x\left(1-\displaystyle\frac{y}{x}\right)^2$ litres
$x\left(1-\displaystyle\frac{y}{x}\right)^{n-1}$ litres
$x\left(1-\displaystyle\frac{y}{x}\right)^3$ litres

Problem 4

What number should come next in the sequence, 6, 18, 72, 360, 2160...?

15120
12120
13120
14120

Problem 5

A pump can fill a tank with water in 2 hrs. Because of a leak developed in the tank, it takes now $2\displaystyle\frac{1}{2}$ hrs to fill the tank. The leak will empty the full tank with pump not running, in,

$8$ hrs
$10$ hrs
$14$ hrs
$2\displaystyle\frac{1}{3}$ hrs

Problem 6

Gold is 19 times as heavy as water and copper is 9 times as heavy as water. The ratio in which these two metals are to be mixed so that the mixed alloy becomes 15 times as heavy as water is,

2 : 3
1 : 2
3 : 2
19 : 135

Problem 7

A student was asked to divide a number by 3, but instead of dividing he multiplied it by 3 and got 29.7 as the result. The correct answer would be,

Problem 8

Which of the following fractions is the largest?

$\displaystyle\frac{7}{8}$
$\displaystyle\frac{63}{80}$
$\displaystyle\frac{31}{40}$
$\displaystyle\frac{13}{16}$

Problem 9

A fisherman can row 2 km against the stream in 20 minutes and return in 15 minutes. The speed of the boat in still water is,

$2$ km per hour
$3$ km per hour
$1\displaystyle\frac{1}{2}$ km per hour
$7$ km per hour

Problem 10

Two trains running in opposite direction cross a man standing on the platform in 27 secs and 17 secs respectively and they cross each other in 23 secs. The ratio of their speeds is,

1 : 3
3 : 2
2 : 3
3 : 4