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Question
A box contains 90 discs which are numbered 1 to 90. If one disc is drawn at random from the box, find the probability that it bears a 2-digit number less than 40.
Solution
Total number of the discs which are numbered from 1 to 90
∴ Total number of outcomes = 90
Let A be the event that one disc drawn at random from the box bears a two-digit number
Number of discs that bears a two-digit number = 90 − 9 = 81
Probability of 2-digit number less than 40 are = 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39
Number of discs that bears a two-digit number less than 40 = 30
Favourable number of outcomes = 30
∴ P(A) = `"Favourable number of outcomes"/"Total number of outcomes"`
∴ P(A) = `30/90`
∴ P(A) = `1/3`
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