2.1.4 Estimate quantities to a tolerance acceptable in the context of the estimation

Example 1: Estimating and measuring length

Question

John needs to measure the width of a window, to find out how much material he needs to buy to make a curtain. The curtain material costs R 55 per metre. John estimates the width of the window (using his arm) to be 1,9 metres wide. If Carl goes to the shop with this estimate:

1. How many metres of material would he need to buy?

2. How much would the material cost?

Answer

1. John needs to buy 2m of material

2. 2 × R 55 = R 110

John decides to double-check his estimated measurement before he buys the material and uses his tape measure to accurately measure the width of the window. He determines that the window is
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6 ℓ = 6000 ml

6000 ml ÷ 250 ml = 24

There are 24 cups of water left in the urn.

6 ℓ/20 ℓ×100=30%

The urn is 30% full

Example 4: Measuring temperature

The following weather report appears in the local newspaper in George, in the Western Cape. It gives the expected temperatures for one day in winter.

Study it and answer the questions that follow:

1. For which two South African provinces does this weather map show temperatures?

2. Explain why there are two temperatures given next to each town.

3. Which is the coldest town?

4. Which is the warmest town?

5. What is the difference between the two temperatures given for Alexander Bay?

6. What is the difference between the two temperatures given for De Aar?

7. Based on your own experience, at what time of day is it usually the coldest? (I.e. at what time of day is the minimum temperature likely to be reached?)

8. Joe is planning to drive from Cape Town to Beaufort West on the day for which these temperatures are forecast. Should he pack warm clothes? Explain your answer.

Answer

1. The Western and Northern Cape

2. The first temperature is the expected minimum temperature and the second one is the expected maximum temperature.

3. Kimberley.

4. George.

5. 15°C - 5°C =