### Video Transcript

48 seconds have gone by. How many seconds are left until a
minute passes?

In this picture, we can see one of
the pieces of equipment we can use to measure periods of time, a stopwatch. Now there are two main kinds of
stopwatches. There are those that are digital
and those that have a hand that goes all the way around the clock face, like this
one. I suppose we could call it an
analog stopwatch. This particular stopwatch has got a
red hand. And we can see that it’s traveled
almost all the way around the clock face. Can you see where it started? Well, the blue area shows where
it’s traveled. So we can see it began by pointing
directly upwards to the number 60. Then someone must have pressed the
start button to start timing. The hand then moved around the
clock face. And now it’s at this point here, 48
seconds later.

Obviously, we can see in the first
sentence that 48 seconds have gone by. But we could also tell this by
looking at the clock face. Do you notice anything about the
numbers on this clock face? Instead of being numbered from one
to 12 as they are on an analog clock, our stopwatch is numbered in multiples of
five, all the way up to 60. This is because this stopwatch is
used for measuring very short periods of time, in seconds. So even if we didn’t have this
first sentence to help us, we could still read our stopwatch and see that 48 seconds
have gone by. Five, 10, 15, 20, 25, 30, 35, 40,
45. Now we’ve made all the jumps of
five seconds that we can. If we made another, we’d have gone
too far.

But we have got some more notches
to count. So let’s carry on counting from 45
in ones. 46, 47, 48. So we can see from our second hand
that 48 seconds have passed. But we are asked how many seconds
are left until a minute passes. To solve this problem, we need to
remember a fact about seconds and minutes. One minute is equal to 60
seconds. That’s why our stopwatch goes all
the way up to 60. You know, we could even alter the
wording of our question here. Because both measurements are in
seconds, it’s much easier to work out the answer. If one minute is worth 60 seconds
and 48 of those 60 seconds have gone by, the answer to our problem is going to be
the difference between 60 and 48.

We could find the answer by using
subtraction, maybe starting at 60 and counting backwards until we get to 48. Or let’s use our stopwatch to help
us. Let’s start at 48 seconds and see
how many jumps we need to make to get to 60. And you know, we could do it in two
jumps. First, we could start on 48 and
jump to a nice round number. 48 plus two takes us to 50. And from here, it’s only 10 more
seconds until we get to 60. We’ve counted on two seconds and
then another 10. That’s 12 altogether. We know that 60 seconds are the
same as a minute. And so if 48 seconds have gone by,
we can work out how many seconds are left until a minute passes by counting on from
48 to 60. There are 12 seconds left.