John is 5ft tall and is standing in the light of a 15ft lamppost. His shadow is 4ft long. He walks 1ft father away from the lamppost, by how many feet will his shadow lengthen?

The shadow lengthened by 2.25 ft.

Step-by-step explanation:

Height of the lamppost is not needed here.

We can write the ratio as,

5 / 4 = x/5

25 = 4x

x = 25 / 4

Now it is not needed to find the length of the new shadow, and so, we need to find the length of the added shadow.

25 / 4 - 16 / 4 = 25 - 16 / 4 = 9/4 = 2.25 ft

Length of the new shadow is 25 / 4 = 6.25 ft

So length of new shadow - length of old shadow = 6.25 - 4 = 2.25 ft shadow lengthened