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Total numbers of elementary events are: 51

Since the common difference between the consecutive number is same: 2

It forms an A.P.

First number = a = 1

d = common difference = 3 -1 = 2

Last number = an = 90

an = a + (n-1) d

101 = 1 + (n-1)2

101 -1 = (n-1)2

100/2 = n-1

50 + 1 = n

51 = n, being number of terms

(i) Let E be the event of drawing a number less than 19

The favourable numbers are: 1, 3, 5, 7, 9, 11, 13, 15, 17,

The numbers of favourable outcomes = 9

P (number less than 19) = P (E) = 9/51

(ii) Let E be the event of getting a prime number less than 20

The favourable numbers are: 2, 3, 5, 7, 11, 13, 17, 19

Then, the numbers of favourable outcomes = 8

P (prime number less than 20) = P (E)= 8/51

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