Explanation

Floor changes: 10 → 9 → 11 → 8 → 12 → 7 → 13

Net change = −1 + 2 − 3 + 4 − 5 + 6 = +3

Starting from the 10th floor, the elevator reaches the 13th floor.

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Explanation

The number of circular arrangements of n distinct people is (n − 1)!

For 5 children: (5 − 1)! = 4! = 24

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Explanation

Each office has 8 seats.

To fit 34 people:

34 ÷ 8 = 4 offices with 32 seats, and you’ll still need 2 more seats.

So you need 5 offices.

4 offices = 32 seats  

5 offices = 40 seats → enough for all 34 people

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Explanation

15 men × 20 days = 300 man-days (total work)

Now, with 25 men:

300 man-days ÷ 25 men = 12 days

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Explanation

Let son's present age = x years

Then father's present age = x + 24 years

After 2 years:

Son's age = x + 2

Father's age = x + 24 + 2 = x + 26

Given, After 2 years father's age = 2 _ son's age

So, x + 26 = 2 _ (x + 2)

x + 26 = 2x + 4

26 - 4 = 2x - x

22 = x

Son's present age = 22 years

Father's present age = x + 24 = 22 + 24 = 46 years

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