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NCERT Solutions for Class 5th Maths Chapter 8 Cost of groceries, and using double number lines for buying — Let Us Do

Book page 112–113 Updated on2026-09-19

Q1.
The cost of some grocery items is given in the following table. Find the total cost of each item.
ItemWeightCost of 1 kgTotal cost
Rice12 kg 500 g₹ 60 
Flour7 kg 250 g₹ 40 
Sugar5 kg₹ 45 
Chana dal3 kg 600 g₹ 70 
Besan4 kg₹ 60 
Jaggery1 kg 400 g₹ 50 
The grocery table printed on page 112. The last column is empty — that is what you have to find.
Answer

Rice ₹750, Flour ₹290, Sugar ₹225, Chana dal ₹252, Besan ₹240, Jaggery ₹70.

For each item, work out the cost of the whole kilograms first, then the cost of the extra grams, and add.

  1. Cost of the whole kilograms = number of kg × cost of 1 kg.
  2. Cost of the extra grams: 500 g is half a kilogram, 250 g is one-fourth, 400 g is four-tenths, 600 g is six-tenths. Take that share of the 1 kg price.
  3. Add the two parts.
ItemWeightCost of 1 kgWorkingTotal cost
Rice12 kg 500 g₹6012 × 60 = 720; half of 60 = 30; 720 + 30₹750
Flour7 kg 250 g₹407 × 40 = 280; one-fourth of 40 = 10; 280 + 10₹290
Sugar5 kg₹455 × 45₹225
Chana dal3 kg 600 g₹703 × 70 = 210; 600 g costs 6 × 7 = 42; 210 + 42₹252
Besan4 kg₹604 × 60₹240
Jaggery1 kg 400 g₹501 × 50 = 50; 400 g costs 4 × 5 = 20; 50 + 20₹70
Where “6 × 7” comes from: 100 g is one tenth of a kilogram. So 100 g of chana dal costs ₹70 ÷ 10 = ₹7. Then 600 g costs 6 × ₹7 = ₹42. The same idea gives jaggery: 100 g costs ₹5, so 400 g costs ₹20.
Bill total = 750 + 290 + 225 + 252 + 240 + 70 = ₹1,827
Check one of them a second way: Rice — 12 kg 500 g = 12,500 g. 1,000 g costs ₹60, so 100 g costs ₹6, so 12,500 g costs 125 × ₹6 = ₹750 ✓
Q2.
4 people need 500 g rice for a meal. How much rice will be needed for 8 people if they eat similar quantity of rice? Complete the double number line below.
4 people8 people500 g………g×2×….
The double number line printed on page 112. Fill in the missing weight and the missing multiplier.
Answer

8 people will need 1,000 g of rice, that is 1 kg.

  1. Look at the people. 4 people become 8 people. 4 × 2 = 8, so the number of people is doubled.
  2. Do the same to the rice. Whatever you do on the top line, do on the bottom line. So the rice is doubled too.
  3. Double the rice. 500 g × 2 = 1,000 g.
  4. Say it in the bigger unit. 1,000 g = 1 kg.
4 people8 people 500 g1,000 g = 1 kg × 2 × 2
The missing multiplier at the bottom is the same as the one on top: × 2.
4 people → 500 g
People × 2, so rice × 2
500 g × 2 = 1,000 g = 1 kg
The missing arrow is × 2
Try this: How much rice for 12 people? 12 is 4 × 3, so the rice is 500 g × 3 = 1,500 g = 1 kg 500 g.
Q3.
5 kg of tomatoes cost ₹73. How much will 10 kg of tomatoes cost? Complete the double number line below.
5 kg10 kg₹ 73₹ ………×2×….
The double number line printed on page 113. Fill in the missing cost and the missing multiplier.
Answer

10 kg of tomatoes will cost ₹146.

  1. Look at the weight. 5 kg becomes 10 kg. 5 × 2 = 10, so the weight is doubled.
  2. Double the cost too. The missing arrow is × 2.
  3. Work it out. ₹73 × 2. Split it: 70 × 2 = 140 and 3 × 2 = 6.
  4. Add. 140 + 6 = ₹146.
5 kg → ₹73
Weight × 2, so cost × 2
₹73 × 2 = ₹140 + ₹6 = ₹146
Why doubling is fair: Twice as many tomatoes must cost twice as much money, because every kilogram costs the same. This is the whole idea of a double number line — the two lines move together.
Check it yourself: ₹146 ÷ 2 = ₹73 ✓ Halving the money gives back the price of 5 kg.
Q4.
Nitesh is a scrap dealer. How much would he have paid for (a) 16 kg of old newspaper, if he paid ₹8 for every 1 kg of newspaper? (b) 20 kg iron, if he paid ₹200 for every 10 kg of iron? (c) 10 kg plastic, if he paid ₹30 for 5 kg of plastic? Make double number lines for answering (b) and (c).
Answer

(a) ₹128   (b) ₹400   (c) ₹60

(a) Newspaper — the price is given for 1 kg, so just multiply.

  1. 1 kg costs ₹8.
  2. 16 kg costs 16 × ₹8.
  3. 16 × 8 = 128. So he paid ₹128.

(b) Iron — use a double number line.

10 kg iron20 kg iron ₹200₹400 × 2 × 2
20 kg is double 10 kg, so the money doubles as well.
10 kg → ₹200
20 kg is 10 kg × 2
So the money is ₹200 × 2 = ₹400

(c) Plastic — use a double number line again.

5 kg plastic10 kg plastic ₹30₹60 × 2 × 2
10 kg is double 5 kg, so ₹30 becomes ₹60.
(a) 16 × ₹8 = ₹128
(b) ₹200 × 2 = ₹400
(c) ₹30 × 2 = ₹60
Did you know? A scrap dealer (kabadiwala) buys old newspaper, iron and plastic and sends them to be used again. Notice that iron fetches ₹20 for a kilogram (₹200 for 10 kg) while plastic fetches only ₹6 a kilogram — the price depends on what the scrap can be turned into.
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