I need help solving this

Question

Nico is saving money for his college education. He invests some money at 9?%, and ?$1400 less than that amount at 4%. The investments produced a total of ?$217 interest in 1 yr. How much did he invest at each? rate?

Answer 1

If the interest is compounded annually, and we are only dealing
with 1 year... the simple interest formula can be used.  If the
interest is compounded anything other than annually, we need
to use the compound interest formula.   I am going to assume

this interest is annual and thus we can use  I=prt

 

Let x = amount invested at 9%

x-1400 = amount invested at 4%

I = 217 = interest at 9% plus the interest at 4%

 

217 = x(.09)(1) + (x-1400)(.04)(1)

217 = .09x + .04x - 56

217 + 56 = .13x

 

x = 273/.13 = $2,100 at 9%

2100-1400 = $700 at 4%