Shopping and cooking problems

Real-life maths often mixes weight, capacity, and rupees. A shopkeeper sells dal per kg. A petrol pump sells petrol per litre. A cook follows a recipe per gram. Let's tackle some real-life word problems.

What is this?

The trick to any word problem is:

1. Read twice. Once for the story, once for the numbers.
2. Note down all the numbers with their units.
3. Identify the operation , add, subtract, multiply, or divide.
4. Calculate.
5. Check the answer makes sense.

A clue word like "in total" or "altogether" suggests add. "How much more / less" suggests subtract. "Each", "per", or repeated amounts suggest multiply or divide.

For example: "Dal costs ₹85 per kg. Find the cost of 4 kg." Here "per kg" + "4 kg" means multiply. 85 × 4 = ₹340.

Or: "A 5-litre oil can costs ₹600. Cost per litre?" Total ÷ total. 600 ÷ 5 = ₹120.

Or mixing units: "Sugar in a packet is 250 g. How many packets in 1 kg?" Convert first. 1 kg = 1,000 g. 1,000 ÷ 250 = 4 packets.

Cooking is a great place for these problems. A recipe for one dosa uses 100 g rice and 25 g dal. For 8 dosas? Multiply each by 8: 800 g rice and 200 g dal.

Worked examples

Example 1. Rice is ₹52 per kg. Cost of 6 kg?

• 52 × 6 = ₹312.

Example 2. A jar of honey holds 750 ml. Three such jars are bought. Total honey?

• 750 × 3 = 2,250 ml = 2 l 250 ml.

Example 3. A 12-litre oil can is sold at ₹1,440. Price per litre?

• 1,440 ÷ 12 = ₹120 per litre.

Try it

1. Sugar costs ₹45 per kg. Find the cost of 7 kg.
2. Milk packets of 500 ml each cost ₹28. Cost of 5 packets?
3. A 2-litre juice bottle costs ₹220. Price per litre?
4. Rice , 250 g per child for lunch. How much for 40 children?
5. Asha buys 3 kg 500 g of dal at ₹120 per kg. How much does she pay?

Hands-on

Make a bill. Pretend you are a shopkeeper. List 5 items with weight or volume and a rate per kg/litre. Multiply to find the cost of each. Add them all up. Hand the "bill" to a family member.

Recipe for two. Find a small recipe (chapati, rice, dal). It feeds 4 people. Adjust the amounts for just 2 people (divide each ingredient by 2). Write the new recipe.