18. a)9/8,7/8,3/8,17/8,1/8 → 17/8,9/8,7/8,3/8,1/8

b)6/9,6/14,6/7,6/11,6/8 → 6/7,6/8,6/9,6/11,6/14

c)3/6,3/4,5/10 → 5/60,3/60,3/60

d)8/4,4/2,6/3 → 8/12,6/12,4/12

19. a)3/4 + 5/6 + 6/8 = 18 + 20 + 18/24 = 56/24 = 28/12 = 14/6 = 7/20

b)6/10 - 2/8 = 24 - 10/40 = 14/40 = 7/20

c)7/8 + 3/6 - 5/12 = 21 + 12 - 10/24 = 23/24


20. a)5/8.3/9.4/6 = 60/432 = 30/126 = 15/108 = 5/36

b)5/4.3/4.7/4 = 105/64

c)7/9 ÷ 6/4 = 7/9.4/6 = 28/54 = 14/27

21. 3/4 de 60 matemáticas

3/4.60/1 = 180/4 = 90/2 = 45/1 = 45 min

2/3 de 60 natural

2/3.60/1 = 120/3 = 40/1 = 40 min

4/6 de 60 lenguaje

4/6.60/1 = 240/6 = 120/3 = 40/1 = 40 min

3/8 de 60 ingles

3/8.60/1 = 180/3 = 60/1 = 60 min

45 + 40 + 40 + 60 = 185 osea 3 horas con 5 minutos

22. 7/2 kilos de fresas recogidas

7/2 - 3/4 = 14 - 3/4 = 11/4

R/le quedan 11/4 de fresas

23. 8/1.3/4 = 24/4 = 12/2 = 6/1 = 6

R/se han comprado 6 kilos de melocotón

24. 24/1 ÷ 3/4 = 24/1.4/3 = 96/3 = 32/1 = 32

R/obtendremos 32 botellas de vino.