Question 171715

Interest(I)=Principal(P)*Rate(R)*Time(T)

Let x=amount invested at 8%
Then 9000-x=amount invested at 9%
Interest at 8%=x*0.08*1=0.08x
Interest at 9%=(9000-x)*0.09*1=0.09(9000-x)
And we are told that the above interest adds up to 770, so:
0.08x+0.09(9000-x)=770  get rid of parens
0.08x+810-0.09x=770  subtract 810 from each side
0.08x+810-810-0.09x=770-810  collect like terms
-0.01x=-40  divide each side by-0.01
x=$4000--------------------amount invested at 8%
9000-x=9000-4000=$5000---------amount invested at 9%
CK
0.08*4000+0.09*5000=770
320+450=770
770=770

Hope this helps---ptaylor