Question

An investment of $27,000 was made by a business club.The investment was split into three parts and lasted for 1 year.The first part earned 8% interest,the second 6% and the third 9%.total interest from the investment was $2130.the interest from the first investment was three times the interest from the second find the amounts of the three parts of investments

Answer 1

first investment ---- x
2nd investment --- y
3rd investment --- z

.08x + .06y + .09z = 2130 ---> 8x+6y+9z = 213,000 **
x+y+z = 27,000 ***

given: .08x = 3(.06)y
8x = 18y
y = 4x/9
sub into ** 8x+6x+9z = 213,000
8x + 8x/3 + 9z = 213,000
32x + 27z = 639,000 ##

sub into *** x+y+z = 27,000
x + 4x/9 + z = 27000
9x + 4x + 9z = 243,000
13x + 9z = 243,000 ###

3 times ### ---> 39x + 27z = 729,000
subtract ##
7x = 90,000
x = 90,000/7

find y, then backsub into ***