EXERCISE 2.2
1). Find the sum by suitable rearrangement.
a) 837 + 208 + 363 b) 1962 + 453 + 1538 + 647
Ans. = 837 + 363 + 208 Ans. = 1962 + 1538 + 453 + 647
= (837 + 363) + 208 = (1962 + 1538) + (453 + 647)
= 1200 + 208 = 3500 + 1100
= 1,408 = 4,600
2). Find the product by suitable rearrangement
a) 2 x 1768 x 50 b) 4 x 166 x 25
Ans. = (2 x 150) x 1768 Ans = 4 x 25 x 166
= 100 x 1768 = 100 x 166
= 1,76,800 = 16,600
c) 8 x 291 x 125 d)625 x 279 x 16
Ans = 8 x 125 x 291 Ans. = (625 x 16) x 279
= 1000 x 291 = 10000 x 279
= 2,91,000 = 2,79,0000
e) 285 x 5 x 60 f) 125 x 40 x 8 x 25
Ans. = 285 x (5 x 60) Ans. = (125 x 8) x (40 x 25)
= 285 x 300 = 1000 x 1000
= 85,500 = 10,00,000
3). Find the value of the following:
a)297 x 17 + 297 x 3 b)54,279 x 92 + 8 x 54,279
Ans. = 297 x (17 +3) Ans. = 54,279 x (92 + 8)
= 297 x 20 = 54,279 x 100
= 5,940 = 54,27,900
c)81,265 x 169 – 81,265 x 69 d)3,845 x 5 x 782 + 769 x 25 x 218
Ans. = 81,265 x (169 – 69) Ans. = 3,845 x 5 x 782 + 769 x 5 x 5 x 218
= 81,265 x 100 = 3,845 x 5 x 782 + 3845 x 5 x 5 x 218
= 81,26,500 = 3,845 x 5 x (782 + 218)
= 19,225 x 1000
= 1,92,25000
4). Find the product using suitable properties.
a)738 x 103 b) 854 x 102
Ans. = 738 x (100 + 3) Ans. = 854 x (100 + 2)
= 738 x 100 + 738 x 3 = 854 x 100 + 854 x 2
= 73800 + 2214 = 85400 + 1708
= 76,014 = 87,108
c)258 x 1008 d)1005 x 168
Ans. = 258 x (1000 +8) Ans. = (1000 + 5) x 168
= 258 x 1000 + 258 x 8 = 168 x 1000 + 168 x 5
= 258000 + 2064 = 168000 + 840
= 2,60,064 = 1,68,840
5). A taxi-driver filled his car petrol tank with 40 litres of petrol on Monday. The next day, he filled the tank with 50 litres of petrol. If the petrol costs Rs.44 per litre, how much did he spend in all on petrol?
Ans. Petrol filled on Monday = 40 litres
Petrol filled on Tuesday = 50 litres
Total petrol = 90 litres
Cost of petrol per litre = Rs.44
Therefore, Total money spent on petrol =(40 + 50) x Rs.44
= 90 x 44
= Rs.3960
6). A vendor supplies 32 litres of milk to a hotel in the morning and 68 litres of milk in the evening. If the milk costs Rs.45 per litre, how much money is due to the vendor per day?
Ans. Milk quantity supplied in the morning = 32 litres
Milk quantity supplied in the evening = 68 litres
Cost of milk per litre = Rs.45
Total cost of milk per day = 45 x (32 + 68)
= 45 x 100
= Rs.4500
7). Match the following:
| i)425 x 136 = 425 x (6 + 30 + 100) | a) Commutativity under multiplication. |
| ii)2 x 49 x 50 = 2 x 50 x 49 | b) Commutativity under addition. |
| iii)80 + 2005 + 20 = 80 + 20 + 2005 | c) Distributivity of multiplication over addition. |
Ans. i) c ii) a iii) b