David W. answered • 05/12/17

Experienced Prof

There are two important points:

1. Percent (like 20%) may be written as 20/100 or 1.20 as needed by the problem.

2 A 20% growth is 20% of the current height, so the total height is:

current height + 0.20*(current height) = 1.20*(current height)

Let x = Tim's initial height

Translate:

"Tim grows 15%" means Tim's height becomes

1.15x

"Then, another 20%: means Tim's final height is

1.20*(1.15x)

"and is 121cm tall" means

1.20*(1.15x) = 121 cm

x = 121/(1.20*1.15) cm

**x = 87.7 cm**

**Check:**

**87.7*1.15 = 100.9**

**100.9*1.20 = 121.08**