a

b c

b

a.

6 x 31 x 5

= (6 x 5) x 31

= 30 x 31

= 930

b.

8 x 63 x 5

= (8 x 5) x 63

= 40 x 63

= 2520

c

a) 4 x 78 x 5

= (4 x 5) x 78

= 20 x 78

= 1560

b) 2 x 99 x 5

= (2 x 5) x 99

= 10 x 99

= 990

b

49 : x + 56 : x = 7

(49 + 56) : x = 7

105 : x = 7

x = 105 : 7

x = 15

a

a) (56 - 27) - (11 + 28 - 16) 

= 56 - 27 - 11 - 28 + 16 

= (56 + 16) – (27 + 11 + 28)

= 72 – (38 + 28)

= 72 – 66

= 6

b) 28 + (19 - 28) - (32 - 57) 

= 28 + 19 – 28 – 32 + 57

= (28 – 28) + (19 + 57) – 32

= 0 + 76 – 32

= 76 - 32

= 44