Rounding decimals

Estimation

We can use rounding to help estimate answers to questions. To estimate is to 'guess' to some degree using your knowledge about the question at hand. We use the skill of estimating widely in everyday life, such as estimating lengths of time, amounts of money or actual distances.

Question 6

Jade buys a 500 gram bag of beads at a market. Each bead has a mass of 0.48 grams. Which of these is the best estimate for the number of beads in the 500 gram bag?

a

100

b

250

c

1000

d

2500

Solution

There are two parts to this question. Firstly we need to round 0.48 correct to 1 decimal place and then we use this to estimate how many beads will fit within the 500 gram bag.

1. We round 0.48 to 1 decimal place (tenths)

• 0.48 lies between 0.40 and 0.50.
• As 8 is greater than 5, we round it up to 0.50.

2. We now use estimation techniques to see how many halves go into 500. As there are 500 grams of beads in the bag and each bead is 0.5 grams, we can divide 500 by 0.5.

500 ÷ 0.5 = 1000.

Therefore c is the correct answer to Question 6.

  

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Question 5

Question 7