Question 104922
Let x= how much he would hav to invest at 8%.
10000*.05+.08x=.07(10000+x)
500+.08x=700+.07x
.01x=200 subtract .07x+500 from each side.
x=200/.01= $20,000. divide each side by .01
Check:
10000*.05+20000*.08=500+1600=$2,100.
30000*.07=$2,100.
Ed