Maths Olympiad Prep

Library / /80 of 173

Algebra Difficulty 2.6 Junior Find the answer

Two positive integers x x and y y have xy=24 xy=24 and xy=5 x-y=5 . What is the value of x+y x+y ?

A number or a short expression. Fractions can be typed as 3/2, and spacing doesn't matter.

Solution

The positive integer divisors of 24 are 1,2,3,4,6,8,12,24 1,2,3,4,6,8,12,24 . The pairs of divisors that give a product of 24 are 24×1,12×2,8×3 24 \times 1,12 \times 2,8 \times 3 , and 6×4 6 \times 4 . We want to find two positive integers x x and y y whose product is 24 and whose difference is 5. Since 8×3=24 8 \times 3=24 and 83=5 8-3=5 , then x=8 x=8 and y=3 y=3 are the required integers. Here, x+y=8+3=11 x+y=8+3=11 .

Want a route through all this instead of an archive? The track puts 2,000 problems in a working order, from AMC 10 level to the IMO shortlist.

Source: Omni-MATH, licensed Apache-2.0. Statement and solution reproduced as published; topic and difficulty added by this site.