1)5∆∆∆4∆∆∆∆3∆∆∆∆∆2∆∆∆∆∆∆1∆∆∆∆∆∆∆
1=12/12
1=38/38
1=145/145
1=239/239
2=14/7
5=20/4
9=72/8
7=21/3
3 2/9=29/9
4 1/7=29/7
1 4/15=19/15
3 6/7=27/7
12 2/5 62/5
6 7/9=61/9
28 5/6=173/6
80 3/4=323/4
(3/8 - 2/3) * 48 - (5 - 7 4/7) : 1 13/14 = - 12 2/3
1) 3/8 * 48 - 2/3 * 48 = 18 - 32 = - 14
2) 5 - 7 4/7 = - 2 4/7
3) - 2 4/7 : 1 13/14 = - 18/7 * 14/27 = - 36/27 = - 4/3 = - 1 1/3
4) - 14 - (- 1 1/3) = - 14 + 1 1/3 = - 12 2/3