IBPS RRB PO Prelims 12 sep 2020 Questions and Answers Detailed Explanation

Answer: (c)

Let the total work = 18 units (LCM of 6 and 9)

Efciency of A and B together = $18/6$ = 3

Efciency of A alone = $18/9$ = 2

Efciency of B alone = Efciency of A and B together – Efciency of A alone

= 3 – 2 = 1

Hence, the required number of days = $3/8 x 18$ = $27/4$

Answer: (a)

Let speed of stream = x km/hr

Speed of boat = 4x km/hr

$45/\text"4x - x" - 45/\text"4x + x" = 2$

$45/3x - 45/5x = 2$

$1/x$(15 - 9) = 2

x = $6/2$ = 3

Hence, the speed of stream = x = 3 km/hr.

Answer: (d)

Let the age of A be x years

Six years ago

A’s age = x – 6

A’ s uncle’s age = 6x – 36

Two years hence

A’s age = x + 2

A’s uncle ‘s age = 3x+6

A’ s uncle’s age six years ago + 8 = A’s uncle ‘s age two years hence

6x – 36 + 8 = 3x + 6

6x – 28 = 3x + 6

x = 11.33 years

Hence, the answer is D.

Answer: (a)

The pattern of the series is:

121 + 2 = 123

123 – (2 + 3) = 118

118 + (2 + 3 + 5) = 128

128 – (2 + 3 + 5 + 7) = 111

111 + (2 + 3 + 5 + 7 + 9) = 137

Hence, the answer is A.

Answer: (e)

The pattern of the series is: 77 + 8 × 1 = 85

85 – 8 × 2 = 69

69 + 8 × 4 = 101

101 – 8 × 8 = 37

37 + 8 × 16 = 165

Hence, the answer is E.

Answer: (c)

The pattern of the series is:

20 + 3² = 29

29 + 5² = 54

54 + 7² = 103

103 + 9² = 184

184 + 11² = 305

Hence, the answer is C.