2/5-1/10=aducem la acelasi numitor=(2·2-1)/10=(4-1)/10=3/10
5/9- 1/3=(5-1·3)/9=(5-3)/9=2/9
3/4- 5/8=(3·2-5)/8=(6-5)/8=1/8
1/2- 1/3=(1x3-1x2)/6=(3-2)/6=1/6
3/4- 2/7=(3x7-2x4)/14=(21-8)/14=13/14
3/5-3/7=(3x7-3x5)/35=(21-15)/35=6/35
2/9 - 1/6=(2x2-1x3)/18=1/18
5/12 - 2/9= (3x5-2x4)/36=7/36
7/20 -2/15=(7x3-2x4)/60=13/60
5/6-1/8=(5x4-1x3)/24=17/24