Question

Sarah, amy and liam stand on some weighing scales two at a time.here are the measurements:sarah and amy 70kgsarah and liam 80kgliam and amy 80kghow much does liam weigh?

Answer 1

a+s=70, s+l=80, l+a=80

from the first s=70-a which makes the second:

70-a+l=80

-a+l=10

a=l-10 which makes the third:

l+l-10=80

2l-10=80

2l=90

l=45

So Liam weighs 45 kg.