RRB NTPC Arithmetic and Number Systems 2

Question 1

A shopkeeper marks his goods 25% above cost price and gives a 10% discount. What is his profit percentage?

Accepted Answer

12.5%

Answer

Let CP = 100. MP = 125. SP = 125 × 0.9 = 112.5. Profit% = (112.5-100)/100 × 100 = 12.5%.

Question 2

Find the value of: √(0.0081)

Accepted Answer

0.09

Answer

√(0.0081) = √(81/10000) = √81/√10000 = 9/100 = 0.09.

Question 3

A boat travels 30 km upstream in 6 hours and 30 km downstream in 3 hours. What is the speed of the stream?

Accepted Answer

2.5 km/h

Answer

Upstream speed = 30/6 = 5 km/h; Downstream speed = 30/3 = 10 km/h. Stream speed = (Downstream - Upstream)/2 = (10-5)/2 = 2.5 km/h.

Question 4

The difference between a two-digit number and the number obtained by interchanging its digits is 36. What is the difference between the digits?

Accepted Answer

4

Answer

Let digits be a and b. Original number = 10a+b, reversed = 10b+a. Difference: (10a+b)-(10b+a) = 9(a-b) = 36 → a-b = 4.

Question 5

If A can do a piece of work in 10 days and B can do the same work in 15 days, how many days will they take together?

Accepted Answer

6 days

Answer

A's work per day = 1/10; B's work per day = 1/15. Together = 1/10 + 1/15 = 3/30 + 2/30 = 5/30 = 1/6. So they finish in 6 days.

RRB NTPC Practice Test