# 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 gives40 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!