Answer
No, the event all 3 stocks will increase at least 10% is not unusual.
Work Step by Step
$P(first~stock~will~increase~at~least~10$%$)$ $=0.7$ $P(second~stock~will~increase~at~least~10$%$)$ $=0.55$
$P(third~stock~will~increase~at~least~10$%$)$ $=0.20$
Using the Multiplication Rule for Independent Events (page 282):
$P(all~3~stocks~will~increase~at~least~10$%$)=$
$P(first~stock~will~increase~at~least~10$%$)\times$
$P(second~stock~will~increase~at~least~10$%$)\times$
$P(third~stock~will~increase~at~least~10$%$)=$
$=0.7\times0.55\times0.20=0.077$
$0.077\gt0.05$. The event all 3 stocks will increase at least 10% is not unusual.
