Question

Four tickets numbered 00, 01, 10, 11 are placed in a bag. A ticket is drawn at random and replaced. Again a ticket is drawn at random. The probability that the sum of the numbers on the tickets drawn is $21$

• A. $\frac{1}{4}$
• B. $\frac{1}{8}$
• C. $\frac{1}{16}$
• D. $\frac{1}{12}$

Answer 1

The correct option is B $\frac{1}{8}$

First case $=$ first card is numbered $10$ and second $11$
Second case $=$ first card is numbered $11$ and second $10$
Probability of both $=1/4\ast 1/4+1/4\ast 1/4=1/8$