Question

If two unbiased coins are tossed, then what is the probability of having at least one head?

• A. 0.25
• B. 0.5
• C. 0.675
• D. 0.75

Hint:

For "at least one" probability questions, it is often easier to calculate the probability of the complementary event (i.e., the event that does not meet the condition) and subtract it from 1.

Answer 1

The Correct Option is D

When two unbiased coins are tossed, the possible outcomes are: \[ {HH, HT, TH, TT} \] There are 4 possible outcomes in total. Now, we are asked to find the probability of getting at least one head. The only outcome that does not satisfy this condition is "TT" (both tails). Hence, the complementary event is getting "TT", which occurs with probability: \[ P({TT}) = \frac{1}{4} \] So, the probability of having at least one head is: \[ P({at least one head}) = 1 - P({TT}) = 1 - \frac{1}{4} = \frac{3}{4} = 0.75 \] Thus, the correct answer is option (D) 0.75.