2/5+1/2=? 11/15 - 7/10=? 1/8 * 12/5 =? 12/5 : 15/20=?

2/5 + 1/2  = (2*2 + 1*5)/10 = (4 + 5)/10 = 9/10
11/15 - 7/10  = (11*2 - 7*3)/30 = (22 - 21)/30 = 1/30
1/8 * 2/5 = 2/40 =  1/20
12/5 : 15/20 = 12/5 : 3/4 = 12/5 * 4/3 = 16/5 = 3 1/5