Question

The least no. of times a coin must be tossed so that the probability of getting atleast one head is atleast 0.9 is

• A. 3
• B. 4
• C. 5
• D. 6

Answer 1

Answer: (B)

4

Answer 2

$1 - { } ^ { \mathrm { n } } C _ { 0 } \frac { 1 } { 2 ^ { \mathrm { n } } } \geq 0.9$

$\frac { 1 } { 2 ^ { n } } \leq 0.1$

2ⁿ ≥ 10

n = 4