First slide

Combinations

Question

A box contains two white balls, three black balls and four red balls. In how many ways can three balls be drawn from the box, if atleast one black ball is to be included in the draw?

Moderate

A

64
B

65
C

46
D

None of these

Solution

A selection of 3 balls so as to include atleast one black ball, can be made in the following 3 mutually exclusive ways
(i) The number of ways in which 1 black balls and 2 others are selected $=^{3} C_{1} \times^{6} C_{2} = 3 \times 15 = 45$
(ii) The number of ways in which 2 black balls and 1 other are selected $=^{3} C_{2} \times^{6} C_{1} = 3 \times 6 = 18$
(iii) The number of ways in which 3 black balls and no other are selected $=^{3} C_{3} = 1$
.'. Total numbers of ways = 45 + 18 + 1 = 64

Get Instant Solutions

When in doubt download our app. Now available Google Play Store- Doubts App

Recieve an sms with download link

Doubts App

OR

SCAN ME

Doubts App

Doubts App