Question 144853
let $x be invested at 5% then $(10000-x) be invested at 7%
now interest on $x at 5% will be ={{{ x*5/100}}}
and interest on $(10000-x)       ={{{(10000-x)*7/100}}}
according to condition 
5x/100+7(10000-x)/100=644
(5x+70000-7x)/100=644
-2x=100(644)-70000
-2x=64400-70000
-2x=-5600
2x=5600
x=5600/2
x=2800  hence 2800 is invested on 5% and 7200 on 7%