Originally Posted by

**rgba**
Hi,

I'm going over a book on elementary algebra and came across the following word problem:

**A sum of $2100 is invested, part of it at 3% interest and the remainder at 5%. If the interest earned by the 5% investment is $51 more than the interest earned by the 3% investment, find the amount invested at each rate.**

I tried to solve:

**interest = principal * rate * time**

interest = principal * rate (since time is assumed to be 1)

i = pr

**sum = 2100**

px = 2100 - py

py = ?

rx = 0.03

ry = 0.05

ix = iy - 51

iy = ix + 51

I assumed that the sums of interest parts is equal to the sums of parts and rates, as below:

**ix + iy = px(rx) + py(ry)**

ix + iy = 63 + 0.02py

I just can't solve this problem! Hope you can help out!

Thanks!