Question

Two whole number are randomly selected and multiplied.If the probability that the units place in their product is "Even" is $p$ and the probability that the units place in their product is "Odd" is q then p/q is ?

• A. $4$
• B. $3$
• C. $2$
• D. $1$

Answer 1

The correct option is B $3$

Let the two whole numbers be $a$ and $b$.
q=Probability that $ab$ is odd.
The above is possible if and only if both $a$ and $b$ are odd.
The probability of that happening is: $\frac{1}{2}\times \frac{1}{2}=\frac{1}{4}$
(Probability of $a$ being odd is $0.5$ and same for $b$)
$\therefore q=\frac{1}{4}$
As $p$ is the probability of complementary event, $p=1-\frac{1}{4}=\frac{3}{4}$
$\therefore \frac{p}{q}=3$