Last year, Carmen had $20,000 to invest. She invested some of it in an account that paid 7% simple interest per year, and she invested the rest in an account that paid 6% simple interest per year. After one year, she received a total of $1290 in interest. How much did she invest in each account?
Let
x ------> amount invested an account that paid 7% simple interest per year
20,000-x ------> amount invested an account that paid 6% simple interest per year
Remember that
The formula to calculate the simple interest is equal to
I=P(rt)
in thus problem we have
r1=7%=0.07
r2=6%=0.06
t=1 year
P1=x
P2=20,000-x
I1+I2=1290
x(0.07)(1)+(20,000-x)(0.06)(1)=1,290
solve for x
0.07x+1,200-0.06x=1,290
0.01x=1,290-1,200
0.01x=90
x=9,000
therefore
The amount invested an account that paid 7% simple interest per year was $9,000
and
The amount invested an account that paid 6% simple interest per year was $11,000