A woman invested $15,000, part at 7% annual interest and the rest at 8%. If she earned $1,100 in income over a one-year period, how much did she invest at 7%?

Answer 1

Invested $P @ 7%.
Invested $(15,000-P) @ 8%.

P*r*t + (15000-P)*r*t = $1100.
P*0.07*1 + (15000-P)*0.08*1 = 1100
0.07P + 1200 -0.08P = 1100
-0.01P = 1100-1200 = -100
P = $10,000 @ 7%.