On Earth Day Melody planted a tree that was 4 feet tall. The tree is predicted to grow 2.5 feet per year. How many years will take the tree to reach its maximum height of 39 feet tall?

Answer 1

Introductory math answer: First, we figure out how many feet it has left to grow to reach 39 ft. It's already 4 feet tall, so the amount it needs to grow is the difference between 39 and 4.

39-4=35.

How many sets of 2.5 feet are in 35?

35/2.5=14.

So the tree needs to grow 25 feet 14 times. It needs to grow for 14 years!

Pre-algebra/Algebra answer: This is exactly the same thing, but in a format that will help you graph these kinds of problems on an x-y axis later.

Let's call the height of the tree "y," and the number of years since planting the tree "x."

The height of the tree (y) is 4 feet, plus 2.5 feet for every year (x) since it was planted.

Or in other words, y=2.5x+4

Now we plug in a height of 39, and solve for x!

39=2.5x+4

-4 -4

35=2.5x

(Divide both sides by 2.5 to isolate x): (35)/2.5=(2.5x)/2.5

14=x

The tree needs to grow an additional 14 years!

Answer 2

Starting with a height of 4 feet, the tree would need to grow an additional 35 ft. to reach 39 ft. At a growth rate of 2.5 ft per year, it would take

35 ft.÷ 2.5 ft./y

= 14 years