When a certain tree was first planted, it was 4 feet tall and the height of the tree increased by a constant amount each year for the next 6 years. At the end of 6 year the tree was 1/5 taller than it was at the end of 4 year. By how many feet did the height of the tree increase each year?

When a certain tree was first planted, it was 4 feet tall and the height of the tree increased by a constant amount each year for the next 6 years. At the end of 6 year the tree was 1/5 taller than it was at the end of 4 year. By how many feet did the height of the tree increase each year?

(A) 3/10
(B) 2/5
(C) 1/2
(D) 2/3
(E) 6/5

The “tree” questions comes up about 50% of the time in GMAT tutoring sessions. There’s nothing crazy going on here but you do need to focus on the question and then stay organized in the follow through.

I’d go ahead and draw a little chart to make sense of the information. When the tree was first planted it was 4 feet tall so that’s the start of the number line and then it grew by a constant amount each year so assign a variable for that, say x. Then you can define the 6th year in terms of the 4th year (the 6th year is 5/4ths the 4th year). That’s it. Solve for x. On thing that makes the follow through easier: multiply both sides by 5/6. Why? There’s a 6 on the right side. That creates a nice cancellation. These little moves in and of themselves aren’t critical but this kind of heads up thinking does help you get in the mindset that creates success on the GMAT.

Related GMAT Practice

Here’s another GMAT word problem with some algebra follow through: Alex deposited x dollars into a new account