Three unbiased coins are tossed. What is the probability of getting at most two heads? · ABC26GN5338
Subject: General Aptitude · Chapter: Probability
Three unbiased coins are tossed. What is the probability of getting at most two heads?
(a)$\frac{3}{4}$
(b)$\frac{1}{4}$
(c)$\frac{3}{8}$
(d)$\frac{7}{8}$
Answer
Answer (as printed): D
Explanation
Here $S=\{\mathrm{TTT}, \mathrm{TTH}, \mathrm{THT}, \mathrm{HTT}, \mathrm{THH}, \mathrm{HTH}, \mathrm{HHT}, \mathrm{HHH}\}$. Let $E=$ event of getting at most two heads. Then, $E=\{\mathrm{TTT}, \mathrm{TTH}, \mathrm{THT}, \mathrm{HTT}, \mathrm{THH}, \mathrm{HTH}, \mathrm{HHT}\}$. $$\therefore \quad P(E)=\frac{n(E)}{n(S)}=\frac{7}{8} .$$
Explanation as extracted from the printed page; notation may be imperfect.