maths
posted by joi on .
A rectangle is divided into 4 parts, A B, C and D. The areas of A: B: C are in the ratio 10:18:5. C is a square with an area of 25cm squared. What is the area of rectangle D?

Make a sketch,
let part A be x by y
let part B be x by 5
let part C be 5 by 5 , the square
then part D is 5 by y
xy : 5x : 25 = 10:18:5
so
xy/10 = 5x/18 = 25/5
using 5x/18 = 25/5
5x = 90
x = 18
then in xy/10 = 25/5
18y/10 = 5
y = 50/18 = 25/9
area of D = 5y = 5(25/9) = 125/9 or 13 8/9