NCERT Class X Chapter 14: Probability Exercise 14.1 Question (18)
NCERT Class X Chapter 14: Probability Exercise 14.1 Question 18
Question:
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.
Given:
Total number of discs = 90. Discs are numbered from 1 to 90.
To Find:
(i) Probability of drawing a two-digit number.
(ii) Probability of drawing a perfect square number.
(iii) Probability of drawing a number divisible by 5.
Formula:
Probability = Number of favorable outcomes Total number of outcomes
Solution:
(i) Two-digit numbers are from 10 to 90. Number of two-digit numbers = 90 - 9 = 81
⇒ Probability of drawing a two-digit number =
81
90
=
9
10
(ii) Perfect square numbers between 1 and 90 are 1, 4, 9, 16, 25, 36, 49, 64, 81. Number of perfect squares = 9
⇒ Probability of drawing a perfect square number =
9
90
=
1
10
(iii) Numbers divisible by 5 are 5, 10, 15,..., 90. Number of such numbers = 90/5 = 18
⇒ Probability of drawing a number divisible by 5 =
18
90
=
1
5
Result:
(i) Probability of drawing a two-digit number =
9
10
(ii) Probability of drawing a perfect square number =
1
10
(iii) Probability of drawing a number divisible by 5 =
1
5
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