Đáp án`+`Giải thích các bước giải:
`C1: 7/5+ 2/5 = (7+2)/5 = 9/5 -> D`
`C2: (-3)/4 + (-2)/4 = (-3+(-2))/4 = (-5)/4 -> B `
`C3 : 12/19 + 6/19 = (12+6)/19 = 18/19 -> B`
`C4: 2/5 + 1/3 = 6/15 + 5/15 = 11/15 -> A`
`C5 : 3/4 + (-3)/20 = 15/20 + (-3)/20 = 12/20 = 3/5 -> A`
`C6 : 3/7 . 2/15 = (3.2)/(7.15) = (3.2)/(7.3.5) = 2/(7.5) = 2/35 -> A`
`C7: (-2)/7 . 1/13 = ((-2).1)/(7.13) = (-2)/91 -> D`
`C8: (-4) . (-7)/5 = ((-4).(-7))/5 = 28/5 -> C`
`C9 : x = 5/4 + 3/4 = (5+3)/4 = 8/4 = 2 -> B`
`C10: x = 12/9 + 5/9 = (12+5)/9 = 17/9 -> B`
