Question

Zara wakes up late on average $3$ days in every $5$.
If Zara wakes up late, the probability she is late for school $=\frac{9}{10}$
If Zara doesn't wake up late, the probability she is late for school $=\frac{9}{10}$
Using tree diagram, on what percent of days Zara does not get to school on time?

• A. $34$%
• B. $90$%
• C. $67$%
• D. None of these

Answer 1

The correct option is B $90$%

From the given condition that 'Zara wakes up late on average $3$ days in every $5$' we get that:

P(Waking late ) = $\frac{3}{5}$

P(Not waking late ) = $\frac{2}{5}$

Probability of Zara waking late, reaching school late $=\frac{9}{10}$

Probability of Zara not waking late, reaching the school late = $\frac{9}{10}$

By the tree diagram we have:

$\frac{3}{5}\times \frac{9}{10}+\frac{2}{5}\times \frac{9}{10}=\frac{9}{10}$

Hence percentafe of days Zara doesnot get o school on time =

$\frac{10-1}{10}\times 100=\frac{9}{10}\times 100=90\%$