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15.	In a consignment of eggs 552 were cracked, which was 12 percent of the total consignment. How many eggs were in the consignment?

Answer

4600 (552 ÷ 12) × 100.

16.	A man has 53 socks in his drawer: 21 identical blue, 15 identical black and 17 identical red. The lights are fused and he is completely in the dark. How many socks must he take out to make 100 per cent certain he has a pair of black socks?

Answer

40 socks. If he takes out 38 socks, although it is very unlikely, it is possible they could all be blue and red. To make 100 per cent certain that he also has a pair of black socks he must take out a further two socks;

17.	A box contains 12 marbles of three different colours green, yellow and blue-4 each, If you were to close your eyes and pick them at random, how many marbles must you take out to be sure that there are at least two of one colour among the marbles picked out?

Answer

In the first three pickings you may get 1 of each colour, on the 4th pick there will be at least two of one colour. Therefore,the answer is 4.