An investment of $3,000 is made at an annual simple interest of 5%. How much additional money must be invested at an annual simple interest rate of 8%, so that the total annual interest earned is 7.5 of the original amount that you invested?

Question

My answer: $279,375

Answer 1

.05(3000) + .08x = .075(3000+x)
150 + .08x = 225 + .075x
.005x = 75
x = 15,000

check:
total invested = 3000+15000 = 18000
.075(18000) = 1350

interest at partial investments
= .05(3000) + .08(15000)
= 150 + 1200
= 1350

How did you possible get $279,375 ???
Did that sound logical to you ?