Question

Two whole numbers are randomly selected and multiplied. The probability that the unit's place in their product is $0$ or $5$ is

• A. $\frac{1}{3}$
• B. $\frac{16}{25}$
• C. $\frac{9}{25}$
• D. None of these

Answer 1

The correct option is C $\frac{9}{25}$

A whole number may end with one of 0,1,2,...9 digits. We are selecting two whole numbers at random. If the first number selected ends with 0, the second number can end any if the 10 digits. If the 1st number ends with 1, the second number should end with 0 to 5 i.e 2 digits

The similar way for others except 5 in which the 2nd number can end with any of the 10 digits.

So, the probability $=\frac{10+2+2+2+2+10+2+2+2+2}{10\times 10}=\frac{9}{25}$