(20 - 19 3/7)+(17 3/4 - 17)+ (2 1/2- 17/24)= 3 19/168
1)20 - 19 3/7 =19 7/7- 19 3/7 = 4/7
2)17 3/4 - 17 = 3/4
3)2 1/2- 17/24 = (60- 17) :24= 43/24= 1 19/24
4)4/7 +3/4 =(4*4+3*7 ):28= (16+21):28= 37/28= 1 9/28
5)1 9/28 + 1 19/24= 37/28 + 43/24= (6*37+ 7*43):168= (222+ 301):168=523/168= 3 19/168