Skip to main content
OlympiadHQ

Browse · MATH

Print

jmc

counting and probability junior

Problem

The numbers 1 through 25 are written on 25 cards with one number on each card. Sara picks one of the 25 cards at random. What is the probability that the number on her card will be a multiple of 2 or 5? Express your answer as a common fraction.
Solution
There are even numbers and multiples of in the range to . However, we have double-counted and , which are divisible by both and . So the number of good outcomes is and the probability is .
Final answer
\frac{3}{5}