câu 7: a. = 659,18 - 74,66 - 74,52 = 584,52 - 74,52 = 514
câu 8: a. (x + x + x + x) + (2 + 4 + 6 + 8) = 36
4x + 20 = 36
4x = 36 - 20
4x = 16
x = 16 : 4
x = 4
b. (3/4 + x) x 1/2 = 4/5
3/4 + x = 4/5 : 1/2
3/4 + x = 4/5 x 2
3/4 + x = 8/5
x = 8/5 - 3/4
x = 32/20 - 15/20
x = 7/20