Question

A die is rolled twice and the sum of the numbers appearing on them is observed to be 7. What is the conditional probability that the number 2 has appeared at least once

• A. $\frac { 3 } { 4 }$
• B. $\frac { 1 } { 2 }$
• C. $\frac { 2 } { 3 }$
• D. $\frac { 1 } { 3 }$

Answer 1

Answer: (D)

$\frac { 1 } { 3 }$

Answer 2

sum 7 = {(1, 6), (2, 5), (3, 4), (4, 3), (5, 2), (6, 1)}

$\mathrm { P } \left( \frac { \text { at least } 2 } { 7 } \right)$ = $\frac { 2 } { 6 }$ = $\frac { 1 } { 3 }$