1: 1/2 5/6
2: 19/20 11/18 19/15 5/14
3: ⑴ 1/4+1/3=7/12 ⑵ 1/3-1/4=1/12
4: ⑴ 1/2+3/10=4/5
⑵ 4/5-1/5=3/5
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