问题标题：
【英文数学题要求列方程解答Aninvestorreceived$1400interestperannumfromasumofmoney,withpartofitinvestedat10%andtheremainderat7%simpleinterest.Thisinvestorfoundthatifsheinterchangedtheamountsshehadinvested】
问题描述：
英文数学题要求列方程解答
Aninvestorreceived$1400interestperannumfromasumofmoney,withpartofitinvestedat10%andtheremainderat7%simpleinterest.Thisinvestorfoundthatifsheinterchangedtheamountsshehadinvestedshecouldincreaseby$90perannum.Calculatethetotalamountinvested
龙艳军回答：
Lettheamountsinvestedin10%and7%xandydollarsrespectively:
x*10%+y*7%=1400
x*7%+y*10%=1400+90
y=10000
x=7000
Totalis$17000
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