Question

Charlie's weight is nine kilograms greater than his brother's. Together they weigh 99 kilograms. Let x represent the weight of the little brother. Which equation can be used to determine what each one weighs?
A) x2 + 9 = 99
B) 2x - 9 = 99
C) 2x + 9 = 99
D) 3x - 9 = 99

Answer 1

C=x+9, c+x=99, c=99-x

So we have two equations equal to c, c=x+9 and c=99-x, since c=c:

x+9=99-x

2x+9=99

2x=90

x=45, and since c=x+9, c=54

So Charlie weighs 54 kg and his brother weighs 45 kg.