71.
Let’s calculate.
2.8 ´ 0.7 ¸ 0.4
= 1.96 ¸ 0.4
= 4.9
72.
Let’s calculate.
9.2 ´ 7.2 ¸ 3.6
= 66.24 ÷ 3.6
= 18.4
77.
Solve the following problem.
A pound of cherries costs 18.7 dollars. Mum still has 12.6 dollars after buying 2 pounds. How much did she have initially?
18.7 ´ 2 + 12.6
= 37.4 + 12.6
= 50
She had 50 dollars initially.
78.
Solve the following problem.
A pomelo costs 15.2 dollars. Mr. Chan bought 4 of them and paid 70 dollars. What is his change?
70 - 15.2 ´ 4
= 70 - 60.8
= 9.2
His change is 9.2 dollars.
79.
Solve the following problem.
An apple costs 3.6 dollars. Mum bought 4 of them. If she used the same amount of money to buy oranges which cost 2.4 dollars each, how many oranges can she buy?
3.6 ´ 4 ¸ 2.4
= 14.4 ¸ 2.4
= 6
She can buy 6 oranges.
80.
Solve the following problem.
A rectangular lawn is 4.2 m wide. Its length is 2 times and 0.8 m more than its width. What is the length of the lawn?
4.2 ´ 2 + 0.8
= 8.4 + 0.8
= 9.2
The length of the lawn is 9.2 m.
81.
Solve the following problem.
A kilogram of watermelon costs 7.8 dollars. A kilogram of bananas costs 3.8 dollars. What is the total cost to buy a watermelon of 6.5 kg and 6 kg of bananas?
7.8 ´ 6.5 + 3.8 ´ 6
= 50.7 + 22.8
= 73.5
The total cost is 73.5 dollars.
518.
Solve the following problem.
A lemon costs 3.2 dollars. Mum bought 7 of them and she paid 100 dollars. What is the change?
100 - 3.2 ´ 7
= 100 - 22.4
= 77.6
The change is 77.6 dollars.
519.
Solve the following problem.
Simon has a bottle of orange juice and he equally divided it into 4 glasses. Each glass contains 0.4 L. If he divided the bottle of orange juice into 5 glasses equally, how much does each glass contain?
0.4 ´ 4 ¸ 5
= 1.6 ¸ 5
= 0.32
Each glass contains 0.32 L of orange juice.
520.
Solve the following problem.
Mum divided 1.4 L of fresh milk into 7 glasses equally. She drank 3 glasses of fresh milk. How many litres of fresh milk did she drink?
1.4 ¸ 7 ´ 3
= 0.2 ´ 3
= 0.6
She drank 0.6 L of fresh milk.
521.
Solve the following problem.
Yan has 2.38 m of ribbon. Susan’s ribbon is 0.65 m longer than Yan’s. Wing’s ribbon is 1.7 m shorter than Susan’s. How long is Wing’s ribbon?
2.38 + 0.65 - 1.7
= 3.03 - 1.7
= 1.33
Wing’s ribbon is 1.33 m long.
522.
Solve the following problem.
A kilogram of grapes costs 15.8 dollars. After buying 1.5 kilograms, Mrs. Cheung still has 51.3 dollars. How much did she have initially?
15.8 ´ 1.5 + 51.3
= 23.7 + 51.3
= 75
She had 75 dollars initially.
523.
Solve the following problem.
A pencil costs 1.2 dollars. A ball pen costs 6.7 dollars. What is the total cost of buying 3 pencils and 1 ball pen?
1.2 ´ 3 + 6.7
= 3.6 + 6.7
= 10.3
The total cost is 10.3 dollars.
524.
Solve the following problem.
A dozen of chicken eggs cost 13.2 dollars. A duck egg costs 2 dollars. How much is a chicken egg cheaper than a duck egg?
2 - 13.2 ¸ 12
= 2 - 1.1
= 0.9
A chicken egg is 0.9 dollar cheaper than a duck egg.
525.
Solve the following problem.
A fountain pen costs 299.9 dollars. If two pens are bought together, they only cost 450 dollars. How much is the average cost cheaper than just buying one fountain pen?
299.9 - 450 ¸ 2
= 299.9 - 225
= 74.9
It is 74.9 dollars cheaper.
526.
Solve the following problem.
A box of egg rolls costs 24.5 dollars. Now each box is 3 dollars cheaper. What is the total cost to buy 5 boxes?
(24.5 - 3) ´ 5
= 21.5 ´ 5
= 107.5
The total cost is 107.5 dollars.
527.
Solve the following problem.
A bowl costs 32.9 dollars. A pair of chopsticks costs 26.7 dollars. What is the total cost to buy 4 bowls and 4 pairs of chopsticks?
(32.9 + 26.7) ´ 4
= 59.6 ´ 4
= 238.4
The total cost is 238.4 dollars.
528.
Solve the following problem.
A can of ham costs 5.8 dollars. A can of beef costs 7.3 dollars. What is the total cost to buy 3 cans of ham and 5 cans of beef?
5.8 ´ 3 + 7.3 ´ 5
= 17.4 + 36.5
= 53.9
The total cost is 53.9 dollars.
529.
Solve the following problem.
A hamburger costs 4.9 dollars. A fish-o-fillet costs 8.9 dollars. Peter bought 2 fish-o-fillets and John bought 3 hamburgers. How much more did Peter pay than John?
8.9 ´ 2 - 4.9 ´ 3
= 17.8 - 14.7
= 3.1
Peter paid 3.1 dollars more than John.
530.
Solve the following problem.
5 friends had lunch in a pizza restaurant. They ordered a pizza at 85.9 dollars, a plate of spaghetti at 67.4 dollars and a bottle of coke at 35.7 dollars. How much each has to pay on average?
(85.9 + 67.4 + 35.7) ¸ 5
= 189 ¸ 5
= 37.8
Each has to pay 37.8 dollars on average.
531.
Solve the following problem.
There are 8 buckets of water. One of them contains 10.2 L of water and the other 7 buckets contain 14.8 L each. Now all the water is equally filled into 95 bottles. How many litres of water does each bottle contain? (Give your answer correct to one decimal place.)
(10.2 + 14.8 ´ 7) ¸ 95
= (10.2 + 103.6) ¸ 95
= 113.8 ¸ 95
= 1.2 (Correct to one decimal place.)
Each bottle contains 1.2 L of water.
532.
Solve the following problem.
A pack of potato chips costs 6.5 dollars. There is now a special offer of buy 4 get 1 free. How much is it cheaper per pack if 5 packs are bought on average?
6.5 - 6.5 ´ 4 ¸ 5
= 6.5 - 26 ¸ 5
= 6.5 - 5.2
= 1.3
Each pack is 1.3 dollars cheaper on average.
815.
The 5-sided polygon below is made up of a square, a trapezium and a right-angled isosceles triangle. Solve the following questions.
(a) Find the area of the square .
2.6 ´ 2.6
= 6.76
The area of the square is 6.76 cm2.
(b) Find the area of the trapezium .
(2.6 + 3.8) ´ 1.5 ¸ 2
= 4.8
The area of the trapezium is 4.8 cm2.
(c) Find the area of the right-angled isosceles triangle .
(2.6 ´ 2.6) ¸ 2
= 3.38
The area of the right-angled isosceles triangle is 3.38 cm2.
(d) Find the area of the 5-sided polygon .
6.76 + 4.8 + 3.38
= 14.94
The area of the 5-sided polygon is 14.94 cm2.
816.
Solve the following problem.
A brush costs 7.2 dollars. A ball pen costs 6.6 dollars. What is the total cost of buying 3 brushes and 2 ball pens?
Column form7.2 ´ 3 + 6.6 ´ 2
= 21.6 + 13.2
= 34.8
The total cost is 34.8 dollars. /
817.
Solve the following problem.
Mum has made 1.25 L of juice and she divided it into 5 glasses with 0.2 L of juice left. How much juice does each glass contain on average?
Column form(1.25 – 0.2) ¸ 5
= 1.05 ¸ 5
= 0.21
Each glass contains 0.21 L of juice
on average. /
962.
Solve the following problem.
An iron wire is 1 metre long. Some squares are made with the wire. The length of each side of all squares is 2.4 cm long. How many squares can be made? How many centmetres of the iron wire are left?
100 ¸ (2.4 ´ 4) = 10 … 4
10 squares can be made and 4 cm of iron wire are left.
964.
Mum saw the following advertisement when she was reading a newspaper.
Solve the following problems.
(a) Mum bought 2 cans of pineapples and she paid 20 dollars. How much should she have a change of?
20 – 5.6 ´ 2 = 8.8 .
She should have a change of 8.8 dollars.
(b) Dad bought a can of roast pork and 3 cans of sardines. How much should he pay?
7.3 + 6.7 ´ 3 = 27.4 .
He should pay 27.4 dollars.
(c) How many cans of pineapples can be bought with 20 dollars at most? How much are left?
20 ¸ 5.6 = 3 … 3.2
At most 3 cans of pineapples can be bought with 20 dollars.
3.2 dollars are left.
(d) How many cans of roast pork can be bought with 50 dollars at most? How much are left?
50 ¸ 7.3 = 6 … 6.2
At most 6 cans of roast pork can be bought with 50 dollars.
6.2 dollars are left.
(e) How many cans of pineapples can be bought with the money to buy 5 cans of roast pork? How much are left?
7.3 ´ 5 ¸ 5.6 = 6 … 2.9
The money to buy 5 cans of roast pork can be used to buy at most
6 cans of pineapples. 2.9 dollars are left.
(f) How many cans of lunch meat can be bought with the money to buy 4 cans of sardines? How much are left?
6.7 ´ 4 ¸ 4.5 = 5 … 4.3
The money to buy 4 cans of sardines can be used to buy at most
5 cans of lunch meat. 4.3 dollars are left.