Posted by Adam on .
A half of what John's age was 4 years ago is equal to one third of what it will be in 5 years' time. How old is John now? Explain your workings

Mathematics 
Reiny,
Let John's present age be x
Four years ago John was x4
Half of John's age 4 years ago = (x4)/2
John's age in 5 years from now = x+5
a third of his age 5 from now = (x+5)/3
(x4)/2 = (x+5)/3
crossmultiply
3x  12 = 2x + 10
x = 22
So John is now 22 years old
check:
4 years ago he would have been 18
5 years from now he will be 27
is half of 18 equal to a third of 27 ? YES