As you know, an average is calculated by finding the sum of all the values, and then dividing this by the number of different values (so if there are 3 different results, divide the total by 3).
When we take a reading on a stopwatch, we have to be careful when calculating the average. First you have to convert the value to seconds, then add up. Here's an example:
If I took two readings, one was 3:42:07 (that's 3 minutes, 42.07 seconds) and one was 2:56:39, if we tried calculating the average in minutes, we would probably do (3.4207 + 2.5639) / 2. That would give an answer of 2.9923. 2 minutes and 99 seconds? That can't be right, and it's because there are 60 seconds in a minute, whereas decimals work in 100s.
Instead we need to convert the values to seconds. 3:42:07 becomes 222.07 seconds (because 3 minutes is 180 seconds, and 180 + 42 = 222). 2:56:39 becomes 176.39 seconds. The average is 199.23 seconds.
To be honest, it's probably neater and easier to keep your answer in seconds...
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