Solution:

First shop: 80 pencils
80 * 5 paise = 400 paise = 4 rupees

Second Shop: 1 Pencil
1 * 1 = 1 Rupee

Third Shop: 19 pencils
19 * 5 rupees = 95 rupees

4 + 1 + 95 = 100 rupees.

Solution:

9

Explanation:
5 cartons for large boxes = 5 * 6 = 30 boxes
4 cartons for small boxes = 4 * 9 = 36 boxes

He will need 9 cartons to place 66 boxes.

Solution:

The man is 84 years old.
The son is 49 years old.
The grandson is 7 years old.

Solution:

T = 1
W = 3
O = 8
H = 9
R = 0
E = 4

For the full multiplication, see the figure.

Solution:

84

Explanation:
Let us assume that Adam lived for p years.

p/6 + p/12 + p/7 + 5 + p/2 + 4 = x
=> p = 84.

Therefore, Adam lived for 84 years.

Solution:

25

Distance between Tribe Q and Tribe S = 40km
=> Distance between Tribe Q and Tribe R + Distance between Tribe R and Tribe S = 40km
=> Distance between Tribe Q and Tribe R + (Distance between Tribe Q and Tribe R - 10) = 40 km
=> 2 * Distance between Tribe Q and Tribe R = 50km
=> Distance between Tribe Q and Tribe R = 25km

Solution:

28 is the required number.

28 * 3 - 2 = 82.

Solution:

16

Explanation:
Let the number be p, then the square will be p^2
According to question:
2p = (p/4) + 7
=> 8p = p + 28
=> p = 4

p^2 = 4^2 = 16.

Solution:

80,000.

Explanation:
The distance traveled by each tyre:
4/5 * 1, 00, 000km = 80,000 km.

Solution:

father:72, Son:27

Explanation:
The only single digit prime numbers are 2, 3, 5 and 7.
Let us use the possible combinations and check when the difference comes to be 45.
Son = 23, Father = 32, Difference = 7
Son = 25, Father = 52, Difference = 27
Son = 27, Father = 72, Difference = 45

This stand apt for the requirements. Thus the present age of the father is 72 years and that of son is 27 years.