Q10 of 54 Page 320

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

a two- digit number

Given,

⇒ There are 90 discs in a box.


⇒ Number of outcomes in which discs is selected = 90.


⇒ Discs are numbered from 1 to 90.


∴ total 2 digits numbers = 90 – 9 (∵ 1 to 9 will be one digit numbers)


⇒ Total 2 digits numbers = 81


⇒ favourable outcomes = 81


⇒ Probability that discs bears a two- digit number –


⇒ P(two digit numbers) =


⇒ P(two digit numbers) =


⇒ P(two digit numbers) =


∴ Probability that disc bears two digit number is


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