Sarah invested $10,000, part at 5% and the remainder at 7%. The total annual interest she received was $640. How much did she invest at each rate?

Question

anonymous · Answer

say she invested part of 10000( i will call this as X) at 5%
and 10000-X is at 7%
now X* 5% + (10000 -X) *7% =640

anonymous · Answer

solve for X and you will find out the other part as well

dumbcow · Answer

x+y = 10,000
.05x + .07y = 640

multiply top by -.05
-.05x -.05y = -500
.05x  +.07y = 640
_____________________
0 +.02y = 140
y = 7000
x= 3000