Vien invested $800, part at 9%per annum and the rest at 12% per annum. After one year , the total interest earned was $79.50. How much did Vien invest at each rate
2006-09-24 15:31:16 · 3 answers · asked by m 1 in Science & Mathematics ➔ Mathematics
x = amount invested in 12% dealie
800 - x = amount invested in 9% dealie
soooo
[x * 0.12] + [(800 - x) * 0.09] = 79.5
solve for x:
.12x + [72 - .09x] = 79.5
.03x = 79.5 - 72 = 7.5
x = 7.5 / .03
x = 250
therefore 250 @ 12 %
and 800 - 250 = 550 @ 9%
check:
250 * .12 + 550 * .09 = 30 + 49.5 = 79.5
2006-09-24 15:38:22 · answer #1 · answered by Jeff S 2 · 1⤊ 0⤋
If he invested x at 9% then he invested 800-x at 12%/
In one year he earned .09x at 9% and .12(800-x) at 12%.
Then .09x + .12(800-x) = 79.50
Thus .09x + 96 - .12x = 79.50
so 96 - .03x = 79.50
and 96 - 79.50 = 16.50 = .03x
x = 16.50/.03 = $550 = the amount invested at 9%
and 800 - x = 800 - 550 = $250 + the amount invested at 12%
2006-09-24 15:43:17 · answer #2 · answered by wild_turkey_willie 5 · 0⤊ 0⤋
$550 at 9% and $250 at 12%
2006-09-24 15:36:06 · answer #3 · answered by MateoFalcone 4 · 0⤊ 0⤋