18 9
问题描述：
18 9
—x+—×（770-x）=770-50
19 10
答
原式:18/19X + 9/10*770 - 9/10*X = 720
18/19X - 9/10*X =720 - 9/10*770
190*(18/19X -9/10*X) = 190*(720 - 9/10*770)
180X - 171X = 9X = 5130
X = 570