30 !

используя свойства арифметических действий, вычислите:
1) 1/7(0,14+2,1-3,5)
2) 1/12(4,8-0,24-1,2)
3) (18цел.6/7+21цел.3/4): 3
4) (15цел.5/7+20цел.15/16)*1/5

1)

1/7*(0,14+2,1-3,5) =

= 1/7 * (14/100 + 21/10 - 35/10) =

= 1/7 * 14/100 + 1/7 * 21/10 - 1/7 * 35/10 =

= 1/50 + 3/10 - 5/10 = 1/50 + 15/50 - 25/50 = -9/50   (или  -0,18),

2)

1/12*(4,8-0,24-1,2) =

= 1/12*(48/10 - 24/100 - 12/10) =

= 1/12 * 48/10 - 1/12 * 24/100 - 1/12 * 12/10 =

= 4/10 - 1/50 - 1/10 = 20/50 - 1/50 - 5/50 = 14/50 = 7/25     (или  0,28),

3)

(18 6/7 + 21 3/4) : 3 =

= ((18 + 21) + (6/7 + 3/4)) : 3 =

= (39 + (24/28 + 21/28)) : 3 =

= (39 + 45/28) : 3 = 39 : 3 + 45/28 : 3 =

= 13 + 45/28 * 1/3 = 13 + 15/28 = 13 15/28,

4)

(15 5/7 + 20 15/16 ) * 1/5 =

= ((15 + 20) + (5/7 + 15/16)) * 1/5 =

= (35 + (80/112 + 105/112)) * 1/5 =

= (35 + 185/112) * 1/5 = 35 * 1/5 + 185/112 * 1/5 =

= 7 + 37/112 = 7 37/112