Question

The chances to fail in Physics are 20% and the chances to fail in Mathematics are 10%. What are the chances to fail in at least one subject

• A. 28%
• B. 38%
• C. 72%
• D. 82%

Answer 1

Answer: (A)

28%

Answer 2

Let $P ( B ) = \frac { 10 } { 100 } = \frac { 1 } { 10 }$

Since events are independent and we have to find

$P ( A \cup B ) = P ( A ) + P ( B ) - P ( A ) \cdot P ( B )$

$= \frac { 1 } { 5 } + \frac { 1 } { 10 } - \frac { 1 } { 5 } \times \frac { 1 } { 10 } = \frac { 3 } { 10 } - \frac { 1 } { 50 } = \frac { 14 } { 50 } = \frac { 14 } { 50 } \times 100 = 28 \%$