# 1.3.1 Try some yourself

## Activity 1

Round the numbers below:

- (a) to the nearest 10.

- (b) to the nearest 100.

- (c) to the nearest 1000.

325 089, 45 982, 11 985

### Answer

- (a) 325 090, 45 980, 11 990

- (b) 325 100, 46 000, 12 000

- (c) 325 000, 46 000, 12 000

## Activity 2

Some of the entries in the following table are incorrect. Identify the errors and write down the correct rounding.

##

| Rounded to nearest
--- | ---
Number | 10 | 100 | 1000
254 987 | 254 980 | 254 990 | 255 087
12 345 | 12 350 | 12 400 | 12 000
963 | 960 | 1 000 | 1 060

### Answer

The corrected entries are in bold.

##

| Rounded to nearest
--- | ---
Number | 10 | 100 | 1000
254 987 | 254 990 | 255 000 | 255 000
12 345 | 12 350 | 12 300 | 12 000
963 | 960 | 1 000 | 1 000

## Activity 3

The population of London in 1984 was 6696 000 (to the nearest thousand). Round this to the nearest million.

### Answer

7000 000

## Activity 4

Suppose a friend's heart rate is 68 beats per minute. Use sensible rounding and answer these questions.

- (a) How many heart beats per day?

- (b) How many heart beats per week, month, year?

- (c) How many beats per lifetime?

Interpret your results as if to your friend.

### Answer

- (a) Day: 68 × 60 × 24 = 97 920, i.e. about 100 000 beats per day (rounded to the nearest hundred thousand).

- (b) Week: 97 920 × 7 = 685 440, i.e. about 700 000 beats per week (rounded to the nearest hundred thousand).

- Month: 97 920 × 30 = 2737 600, i.e. about 3 000 000 to nearest million.

- Year: because the numbers now are so big it would be appropriate to use numbers that are approximations, e.g.

- 3 million × 12 = 36 million 40 million.

- (c) Lifetime: A lifetime could last from a very short time to over a hundred years, so an assumption must be made. Supposing it to be 80 years gives

- 40 000 000 × 80 = 3 200 000 000, i.e. approximately 3 billion.

- Your interpretation as if to your friend might be something like:

  - Well Chris, if your heart beats at about 70 beats per minute, this means that it beats about a hundred thousand times a day, about seven hundred thousand times a week, about three million a month and about thirty-six million a year. So if you live to be 80 you would expect your heart to beat about three billion times. No wonder we should be looking after our hearts!

OpenLearn - Rounding and estimation
Except for third party materials and otherwise, this content is made available under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 Licence, full copyright detail can be found in the acknowledgements section. Please see full copyright statement for details.