Find the number of Calories in a grapefruit and an orange.

Question

(1) An orange has 15 more Calories than a grapefruit.
(2) Twenty oranges and ten grapefruit have 1800 Calories.

Answer 1

G = Grapefriut calories, R = oRange Calories

G = R - 15

20R + 10G = 1800

Substitute R - 15 for G and solve for R in second equation. Put that value in the first equation to find G. Check by putting both values in the second equation.