Important for :

1

C

Let the present ages of Kidambi and Srikanth be x years and y years respectively.

As per the question,

(x + 14) + (y + 14) = 2(x + y)

x + y + 28 = 2x + 2y

x + y = 28 **.....(i) **

Also,

y + 8 = x

x – y = 8 **.....(ii)**

Solving eqns (i) and (ii), we get

x = 18 and y = 10

Therefore, Present ages of Kidambi and Srikanth is 18 years and 10 years respectively

Hence, option C is correct.

2

B

The family consists of grandparents, parents and three grandchildren.So, the number of family members = 2 + 2 + 3 = 7

We know,

Average of quantities = | Sum of all quantities |

No. of quantities |

The average age of the grandparents is 70 years. So, the total age of the grandparents = 70 × 2 = 140 years

The average age of the parents is 40 years. So, the total age of the parents = 40 × 2 = 80 years

The average age of the grandchildren is 10 years. So, the total age of the grandchildren = 10 × 3 = 30 years

∴ The average age of the family = |
250 | = 35 | 5 | years |

7 | 7 |

Hence, option B is correct.

3

E

Let Mayank's age be (10x + y) years

Age by reversing the digits = (10y + x) yrs

Now, 10x + y − 18= 10y + x

9x – 9y = 18

x – y = 2..................(1)

Also,

10x+y = 8(x+y) – 6

2x – 7y = –6..........… (2)

Solving equations (1) and (2),

x = 4 , y = 2

Therefore, Mayank's age = 10x + y

= 10(4) + 2

= 42 years

Hence, option E is correct.

4

E

Let the number of boys = the number of girls = nHence, total age of boys = 10n

Let the average age of girls = x

Hence, total age of girls = nx

Total age of the class = 10n + nx + x + 13

Total number of people in the class = n + n + 1 = 2n + 1

Average age of the class = | (10n + nx + x + 13) | = 15 |

(2n + 1) |

Since this is a single linear equation in two variables, a unique solution can't be found.

Therefore, the average age of the girls cannot be determined.

Hence, option E is correct.

5

A

Let the ages of the 3 brothers in completed years be x, y, z.x

Clearly, the three numbers have to be less than 18 since the square of 18 itself is 324.

By trial, we see that 325 = 15

As the product of the ages is less than 1000, the ages have to be 6, 8, 15

The youngest is 6.

Hence correct option (A) is correct.