SOLUTION: Phyllis invested 60000 dollars, a portion earning a simple interest rate of 5 percent per year and the rest earning a rate of 7 percent per year. After one year the total interes

Algebra ->  Linear-equations -> SOLUTION: Phyllis invested 60000 dollars, a portion earning a simple interest rate of 5 percent per year and the rest earning a rate of 7 percent per year. After one year the total interes      Log On


   



Question 1103192: Phyllis invested 60000 dollars, a portion earning a simple interest rate of
5 percent per year and the rest earning a rate of 7 percent per year. After one year the total interest earned on these investments was
3420 dollars. How much money did she invest at each rate?

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +I+ = interest earned @ 5%
+3420+-+I+ = interest earned @ 7%
Let +P+ = Amount invested @ 5%
+60000+-+P+ = amount invested @ 7%
-----------------------------------------
+I+=+P%2Ar%2At+
(1) ++I+=+P+%2A.05%2A1+
(2) +3420+-+I+=+%28+60000+-+P+%29%2A.07%2A1+
---------------------------------------
Plug (1) into (2)
(2) +3420+-+.05P+=+4200+-+.07P+
(2) +.02P+=+780+
(2) +P+=+39000+
and
+60000+-+P+=+60000+-+39000+
+60000+-+P+=+21000+
------------------------------
She invested $39,000 @ 5% and
$21,000 @ 7%
------------------------------
check:
(1) +I+=+.05%2A39000+
(1) +I+=+1950+
and
(2) +3420+-+I+=+21000%2A.07+
(2) +3420+-+I+=+1470+
(2) +I+=+1950+
OK