The ages of three friends are in the ratio 17:5:13. What is the age of the youngest friend if the sum of their ages is 105 years?
Let the ages of three friends be 17r, 5r and 13r. The youngest of these is 5r. We have been given their sum. So (17 + 5 + 13)r = 105. Solving, we get r = 3. The youngest is 5 × 3 = 15 years.