Subject: General Aptitude · Chapter: Probability · Exam: · Marks: · Difficulty:
Three unbiased coins are tossed. What is the probability of getting at least 2 heads?
(a)$\frac{1}{4}$
(b)$\frac{1}{2}$
(c)$\frac{1}{3}$
(d)$\frac{1}{8}$
Answer
Answer (as printed): B
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 least two heads $=\{\mathrm{THH}, \mathrm{HTH}$, HHT, HHH\}. $$\therefore \quad P(E)=\frac{n(E)}{n(S)}=\frac{4}{8}=\frac{1}{2} .$$
Explanation as extracted from the printed page; notation may be imperfect.