Question

Ravi asked his neighbor to water a delicate plant while he is away. Without water, the plant would die with probability $4/5$ and with water, it would die with probability $3/20$. The probability that Ravi’s neighbor would remember to water the plant is $9/10$. If the plant actually died, what is the probability that Ravi’s neighbor forgot to water the plant?

(A) $4/5$

(B) $27/43$

(C) $16/43$

(D) $2/25$

Answer 1

Draw the diagram:

Required probability = $$\begin{align*} \frac{0.1 \cdot 0.8}{0.1 \cdot 0.8 + 0.9 \cdot 0.15} = 0.372 \end{align*}$$

Answer = $16/43$