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Mortality of Coins

The mortality of coins is a term used to indicate how long coins last. Coins getting lost, being damaged or being taken out of New Zealand are factors in the mortality rate. In one sense the coins die, which is why it is called the mortality rate. The rate describes how many coins, out of all the coins used in New Zealand, are lost, damaged, or taken overseas each year. A mortality rate of 14% means 14 out of every coin 100 coins are lost, damaged, or taken out of New Zealand every year. A mortality rate of 8% means 8 coin out of every 100 are taken out of usage.


  1. How many New Zealand coins, out of every 100 coins, do you think are lost, damaged or taken overseas each year?

  2. Which coin do you think has the highest mortality rate and why?

  3. What is the biggest cause of mortality?

  4. How accurately can the mortality rate of coins be worked out?

  5. How do they work out the number of coins that are missing each year?


Interesting Coin Fact

Coins don't stay around for ever. The coin 'mortality rate' is estimated to be around 27 million a year. This is 27 million out of all the coins in circulation. 5 cent coins have a mortality rate of 11% (11 out of every 100 5 cent coins).10 cent coins have a rate of 5% with 20 cent coins and 50 cent coins 4%, (4 out of every 100).

Money Boxes and Saving Coins

A lot of coins are taken out of usage by being saved in piggy banks, money boxes and other containers in people's homes. Some people use this as a way to save money while others do not like carrying coins.


  1. Do you know anyone who saves coins like this?

  2. Where are places coins are saved?

Maths Questions:

  1. If you put 5 coins in a money box every week for one year, how much would you save if you didn't take any out?

  2. What is the most you could save and what is the least you could save?

  3. If 1 person out of every 20 New Zealanders saves coins in some kind of money box at home, and they save on average 5 coins each week, how many coins are saved like this every year? (There are approximately 4 million New Zealanders.)


Click on one of the coins below for more maths questions about saving.



Tourists taking coins out of New Zealand is another factor in the mortality rate. On average New Zealand has approximately 2,000,000 overseas tourists each year. If each tourist took one coin out of the country that is a lot of coins. It is estimated that most tourists take more than one coin out of New Zealand.


  1. If each tourist took 4 coins out of New Zealand, how many coins is this?

  2. If half the tourist took 10 coins each out of the country, how many coins is this?


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