英文数学题 要求列方程解答An investor received $1400 interest per annum from a sum of money, with part of it invested at 10% and the remainder at 7% simple interest.This investor found that if she interchanged the amounts she had invested she could increase by $90 per annum.Calculate the total amount invested
问题描述：
英文数学题 要求列方程解答
An investor received $1400 interest per annum from a sum of money, with part of it invested at 10% and the remainder at 7% simple interest.This investor found that if she interchanged the amounts she had invested she could increase by $90 per annum.Calculate the total amount invested
答
翻译一下再解答
答
设为x，invest y
得到0.1y†0.07（x-y）=1400.
0.1（x-y） 0.07y-1400=90
0.07x-0.03y=1400
0.1x-0.03y=2300
0.03x=900
x=30000
答
Let the amounts invested in 10% and 7% x and y dollars respectively:
x*10% + y*7% = 1400
x*7% + y*10% = 1400 + 90
y = 10000
x = 7000
Total is $17000