The equation would actually be A=4O. There are more apples, so you need to increase the orange count to make them equal.


.15A + .1O = 420

A=4O

_______________

(.15)(4O) + .1O = 420

.7O = 420

O = 600

sparkles3144 wrote:Sue planted 4 times as many apple seeds as she planted orange seeds. 15 percent of the apple seeds grew into trees, and 10 percent of the orange seeds grew into trees. If a total of 420 apple trees and orange trees grew from the seeds, how many orange seeds did Sue plant?

A. 540
B. 600
C. 660
D. 720
E. 760

We can PLUG IN THE ANSWERS, which represent the number of orange seeds planted.
When the correct answer choice is plugged in, the total number of trees will be 420.

D: 720
Since 10% of these 720 orange seeds grow into trees, the number of orange trees = 10% of 720 = 72.
Since 4 times as many apple seeds as orange seeds are planted, the number of apple seeds planted = 4*720 = 2880.
Since 15% of these 2880 apple seeds grow into trees, the number of apple trees = 15% of 2880 = 432.
Total number of trees = 72+432 = 504.
Too many trees.
Since the correct answer choice must be SMALLER, eliminate D and E.

B: 600
Since 10% of these 600 orange seeds grow into trees, the number of orange trees = 10% of 600 = 60.
Since 4 times as many apple seeds as orange seeds are planted, the number of apple seeds planted = 4*600 = 2400.
Since 15% of these 2400 apple seeds grow into trees, the number of apple trees = 15% of 2400 = 360.
Total number of trees = 60+360 = 420.
Success!

The correct answer is B.

Sue planted 4 times as many apple seeds as she planted orange seeds.
Meaning:
For every orange seed planted, 4 apple seeds are planted.
Thus:
O/A = 1/4
A = 4O.