Harness, dickey & pierce, p.l.c. Interview Questions, Process, and Tips

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( b ) 216.90

Correct option is C)
Let be students are consider as child
Let the age of child added later be x years.
average age of 12 children =20 years
∴ Total age of 12 children =20×12=240 years
After one more child is added-
Average of 13 children =20−1=19 years
Average age of 13 children =
13
sum of 12 children+x
​

19=
13
240+x
​

⇒240+x=247
⇒x=247−240=7 years
Hence the age of child added later is 7 years.

13

All books can be arranged in 10! ways. A single pair of books can be taken as a unit and arranged among the 8 others in 9! ways. The pair of books can also be interchanged and therefore rearranged in 2! ways. Thus the probability of the pair always being together is (9!*2!)/10!

325

4/52 * 3/51

required number =H.C.F of (73-25),(97-73) & (97-25)
=H.C.F of 48 , 24 and 72 = 4 (c)

The formula to find number of diagonals (D) given total number of vertices or sides (N) is

N * (N – 3)

D = ———–

2

Using the formula, we get
1325 * 2 = N * (N – 3)
N2 – 3N – 2650 = 0

Solving the quadratic equation, we get N = 53 or -50

It is obvious that answer is 53 as number of vertices can not be negative.

Alternatively, you can derive the formula as triange has 0 diagonals, quadrangel has 2, pentagon has 5, hexagon has 9 and so on……

Hence the series is 0, 0, 0, 2, 5, 9, 14, …….. (as diagram with 1,2 or 3 vertices will have 0 diagonals).

Using the series one can arrive to the formula given above.