A total of 324 coins of 20 paise and 25 paise make a sum of Rs. 71. The number of 25-paise coins is

Clearly, the required number would be such that it leaves a remainder of 1 when divided by 2, 3 or 4 and no remainder when divided by 5. Such a number is 25.

Let number of keepers be x. Then,

Total number of feet = 2 x 50 + 4 x 45 + 4 x 8 + 2x = 2x + 312.

Total number of heads = 50 + 45 + 8 + x= 103 + x.

Therefore (2x + 312) = (103 + x) + 224 or x = 15.

Income on the first day = Re. 1.

Income on the 2nd day = Rs. (1x2) = Rs. 2¹.

Income on the 3rd day = Rs. (2¹ x 2) = Rs. 2² and so on. Thus, Income on the rath day = Rs. 2^n-1.

Therefore Income on the 10th day = Rs. 2⁹.

The seven pieces consist of 6 smaller equal pieces and one half cake piece.

Weight of each small piece = 20 g.

So, total weight of the cake = [2 x (20 x6)]g= 240 g.

Let the father's age be x and the son's age be y.

Then, x - y = y or x = 2y,

Now, x = 36. So, 2y = 36 or y = 18.

Therefore Son's present age = 18 years.

So, son's age 5 years ago = 13 years.

Since the number of carbons is 2, only two copies can be obtained.

Clearly, the black cards are either clubs or spades while the red cards are either diamonds or hearts.

Let the number of spades be x. Then, number of clubs = (7 - x).

Number of diamonds = 2 x number of spades = 2x;

Number of hearts = 2 x number of diamonds = 4x.

Total number of cards = x + 2x + 4x + 7 - x = 6x + 7.

Therefore 6x + 7 = 13 ⟺ 6x = 6 ⟺ x - 1.

Hence, number of clubs = (7 - x) = 6.