Question

There are two covers A and B; each containing paper slips with natural numbers from 1 to 7 written on them. One slip is drawn from each cover. Using them, a two digit number is formed with a number from A in the units place and the number from B in the tens place. How many such two digit numbers can be formed? What is the probability that a two digit number so formed is even?

Answer 1

Number of slip in cover $A=7$
Numbers of slips in cover $B=7$
Numbers formed with a number from cover A in the units place and a number from cover B in the tens place are as follows:

11	12	13	14	15	16	17
21	22	23	24	25	26	27
31	32	33	34	35	36	37
42	42	43	44	45	46	47
51	52	53	54	55	56	57
61	62	63	64	65	66	67
71	72	73	74	75	76	77

Thus, total number of two digit numbers $=7\times 7=49$
Number of two digit even numbers $=7\times 3=21$
P(two digit number so formed is even) $=\frac{21}{49}=\frac{3}{7}$