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in Probability by (65.2k points)

A box contains 90 discs which are numbered from 1 to 90. If one disc is drawn at random from the box, find the probability that it bears 

(i) a two-digit number 

(ii) a perfect square number 

(iii) a number divisible by 5.

1 Answer

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Best answer

Number of discs which are numbered from 1 to 30, n(S) = 90 

(i) A two-digit number : 

Out of 90, one digit number = 9 

∴ 2-digit numbers = 90 – 9 = 81 

∴ 2-digit numbers, n(E) = 81

(ii) A perfect square number : 

1, 4, 9, 16, 25, 36, 49, 64, 81 

∴ n(E) = 9

(iii) A number divisible by 

5 : 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90 . 

∴ n(E) = 18

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