I have a starting amount of $2,125. I invest some of it in a bank that pays 4% a year and some in another back that pays 5% a year. After one year I have earned $100. How much money did I invest in ea
How do I set up the problem when im given the formula I=Prt, but im given two intrest rates in the math problem?
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Answers & Comments
There are 2 values for interest, say R and r, and R = 0.05, r = 0.04
There are 2 values for the amount earned, from the 2 banks, say I and i, and we know I + i = 100
There are 2 values for principal invested, say P and p, and we know P + p = 2125
There is only one value for period, say t = 1
So then I = P * 0.05 * 1 and
i = p * 0.04 * 1 and
I + i = 100 and
P + p = 2125
then
0.05P + 0.04p = 100
P + p = 2125
P = 2125 - p
0.05 ( 2125 - p) +0.04p = 100
106.25 - 0.05p + 0.04p = 100
106.25 - 0.01p = 100
0.01p = 6.25
p = 625
so
P = 2125 - 625 = 1500
so the amounts were $1500 and $625