Đáp án:
Bài 1:
a, `1/3 + 1/4`
` = 4/12 + 3/12`
` = 7/12`
b, `3/5 - 2/7`
` = 21/35 - 10/35`
` = 11/35`
c, ` 5/7 : 2/3`
` = 5/7 xx 3/2`
` = 15/14`
d, `3/5 xx 2/7`
` = 6/35`
Bài 3:
`(12 xx 4 xx 72)/(36 xx 2 xx 9)`
` = (4 xx 2 xx 2)/(1 xx 1 xx 3)`
` = 16/3`