# Question Video: Finding How Many Seconds Have Passed by Considering the Starting Time and the Ending Time Mathematics

Seconds are used to measure a short period of time. Complete the following: In the given activity, jumping jacks take ＿ seconds.

03:10

### Video Transcript

Seconds are used to measure a short period of time. Complete the following: In the given activity, jumping jacks take what seconds.

This question is all about how long it takes to do some jumping jacks. These are a great form of exercise, but you probably wouldn’t want to be doing them for too long. Perhaps that’s why, in this question, the activity’s been measured in seconds. As we’re reminded right at the start here, seconds are used to measure short periods of time. And we need to find out how long these jumping jacks have taken. To help us complete this sentence and find how long these jumping jacks take, we’re given three stopwatches. Or really, as we’re going to find out, it’s the same stopwatch but shown three times.

The first stopwatch is labeled start time. This shows us what the stopwatch looked like when the activity began. And if we want to work out how long something’s taken, we need to know when it started. Our second picture shows us what the stopwatch look like at the end of the activity. Knowing the end time is just as important as knowing the start time with a question like this. Our final picture really just puts these two facts together. The part shaded blue shows us where the hand on the stopwatch has moved. We can see both the start time and the end time. And it’s this third picture that’s probably going to be most useful to us. It shows us exactly how long the activity’s taken or, if we want to use a mathematical word, its duration.

We can see that the hand on the stopwatch started when it was pointing directly upwards at the number 60. There are 60 seconds in one minute, and that’s all the way around the clock face. So we really can think of this clock face as going from zero all the way around to 60 seconds. And when the second hand points to this number at the very start, it’s not pointing to 60, but really to zero. This is really useful to us. Because we’re starting at zero, we just need to look at the end time, and this will tell us how long the activity’s taken. If we look at the end time, we can see that the second hand has moved just past the number 35. There are five seconds between each number on the clock face.

But these are all labeled, so we don’t need to start at zero and count in fives. We can just go straight away to 35 and then count on. Looks like we’re going to have to count on another two more seconds. So we’ll say 35 and then 36, 37. In order to find out how long something lasts or its duration, we need a start time and an end time. We’ve read both the start and the end times on our stopwatch. And we’ve used these to find out the duration of the jumping jacks activity. In the given activity, jumping jacks take 37 seconds.