Question

Four positive integers are taken at random and are multiplied together. Then the probability that the product ends in an odd digit other than 5 is

• A. $\frac{3}{5}$
• B. $\frac{609}{625}$
• C. $\frac{16}{625}$
• D. $\frac{2}{5}$

Answer 1

The correct option is C $\frac{16}{625}$

We want that the product ends in an odd digit other than 5.

This means that the digit at units place in each number is one of digits 1, 3, 7, 9.
$\therefore$ Probability of selecting such a digit in a number at unit's is $=\frac{4}{10}$
Hence, required probability $={\left(\frac{4}{10}\right)}^4=\frac{16}{625}$