college algebra world problem

Question

An investment of $92000 was made by a business club. The investment was split into three parts and lasted for one year. The first part of the investment earned 8% interest, the second 6%, and the third 9%. Total interest from the investments was$ 7200.The interest from the first investment was 4 times the interest from the second. Find the amounts of the three parts of the investment.

Answer 1

a + b + c = 92,000

0.08a + 0.06b + 0.09c = 7200

a = 4b

 

Start substituting.

 

4b + b + c = 92,000

5b + c = 92,000

c = 92.000 - 5b

 

0.08(4b) + 0.06b + 0.09(92,000 - 5b) = 7200

0.32b + 0.06b + 8280 - 0.45b = 7200

0.08b = 1080

b = 13,500

 

a = 4(13,500)

a = 54,000

 

c = 92,000 - (13,500 + 54,000)

c = 24,500