RBI Assistant Prelims 2016-17 (Important Questions-6)

RBI Assistant Prelims 2016-17 (Important Questions-6)

1. Two pipes A and B take 20 hrs and 30 hrs respectively to fill a tank. Now A, B and a pipe C are all opened to fill the tank. If it takes 60 hours to fill the tank, what is the work done by pipe C alone ?

A. empty in 12 hrs
B. fill in 12 hrs
C. empty in 15 hrs
D. fill in 15 hrs
E. empty in 10 hrs

Sol. Since the tank is getting filled in more than 20 and 30 hrs, this means that C is emptying pipe
Let C alone empties in x hrs, then
(1/20 + 1/30 – 1/x) = 1/60
1/x = 1/15
So C empties in 15 hrs.

2. 10 years ago, A’s age was double that of B’s. If the ratio of the present ages of B and A is 3 : 5, find B’s age 5 years hence ?

A. 50
B. 45
C. 35
D. 30
E. None of these

Sol. Let the present ages of B and A are 3x and 5x.
Then, 10 yrs ago, (5x-10) = 2 * (3x-10)
Solve, x = 10
So B present age = 30, after 5 years = 35.

3. Rs 420 was divided between three peoples – A, B, and C. If each of them had been given Rs. 18 less than the actual amount given to them, their shares would become in the ratio of 11 : 18 : 32. Find the actual ratio of their shares respectively ?

A. 4:2:3
B. 2:3:5
C. 2:4:7
D. 3:4:6
E. None of these

Sol. (11x+18) + (18x+18) + (32x+18) = 420
61x = 366
So x = 6
So actual ratio is 11x+18 : 18x+18 : 32x+18
Put value of x

4. An item is sold at a certain selling price. Had the same item been sold at 2/3rd of its actual selling price a loss of 20% is incurred. Find the actual profit made ?

A. 520
B. 450
C. 560
D. 430
E. Can't be determined 

Sol. SP = x
CP = y
New SP = 2x/3
So 20 = (y – 2x/3)/y * 100
We have only one equation with 2 variables.

5. A bag contains 5 blue balls, 3 green balls and 2 white balls. If three balls are chosen at random, what is the probability that the three balls are of same color ?

A. 1/12
B. 1/20
C. 1/10
D. 11/120
E. None of these

Sol. Case1: all blue
5C3/10C3 = 1/12
Case2: all green
3C3/10C3 = 1/120
Case3: all white
This case cannot happen because only 2 white balls are there,
Add both cases.

Directions(5-10): Find the missing numbers in the given series:

6. 3. 7, 9, 23, 121, 839, _

A. 7650
B. 7561
C. 7542
D. 7560
E. 7652

Sol. 7*1 + 2 = 9
     9*3 - 4 = 23
    23*5 + 6 = 121
   121*7 - 8 = 839
   839*9 + 10 =7561

7. 6, 8, 16, 34, 66, _

A. 120
B. 122
C. 115
D. 116
E. 124

Sol. 6 + 2*1^2 = 8
     8 + 2*2^2 = 16
    16 + 2*3^2 = 34
    34 + 2*4^2 = 66
    66 + 2*5^2 = 116

8. 90, 89, 58, 53, 34, _

A. 22
B. 24
C. 25
D. 26
E. 21

Sol. 10^2 - 10 = 90
      9^2 + 8  = 89
      8^2 - 6  = 58
      7^2 + 4  = 53
      6^2 - 2  = 34
      5^2 + 0  = 25

9. 50, 26, 14, 8, 5, _

A. 4
B. 3
C. 3.5
D. 2.5
E. 4.5

Sol. 50/2 + 1 = 26
     26/2 + 1 = 14
     14/2 + 1 = 8
      8/2 + 1 = 5
      5/2 + 1 = 3.5

10. 11, 15, 29, 59, 111, _

A. 191
B. 193
C. 192
D. 198
E. 196

Sol. A

    15 - 11 = 4
    29 - 15 = 14
    59 - 29 = 30
    111 - 59 = 52  
    Now finding the difference of the difference,
    14 - 4 = 10
    30 - 14 = 16
    52 - 30 = 22
    Further calculating the difference
    16 - 10 = 6

    22 - 16 = 6

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