Video Transcript
Start Times to the Nearest Five
Minutes
In this video, we will learn how to
count in fives on a clock or a number line to find the duration of events in
minutes.
These children are enjoying their
morning break time. Their break time starts at 11
o’clock, and their morning break time ends at 11:15. How long did that break time
last?
Did you notice that the minute hand
on the clock started at number 12? This means it’s something
o’clock. Then, it moved around the clock to
number three, which is quarter past 11 or 11:15. We can shade the clock to show how
many minutes have passed from 11 to 11:15. We need to count in fives because
each of the numbers on the clock is worth five minutes.
So, from 12 to one, there are five
minutes. And from one to two, there are five
minutes. And from the numbers two to three,
there’s another five minutes. So, let’s count in fives: five, 10,
15. So, morning break time lasts for 15
minutes. The duration of morning break time
is 15 minutes. So, the duration means how long
morning break time lasts. If morning break time starts at 11
and finishes at 11:15, its duration is 15 minutes.
If afternoon break time ends at
2:15 or quarter past two and lasts for 15 minutes, what time does afternoon break
start?
In this problem, we know the end
time, but we don’t know the start time. We know that break time ends at
2:15, but we also know that break time lasts for 15 minutes. So, we could start at 2:15 and
count back 15 minutes on our clock face. Five, 10, 15. The minute hand started at number
three and moved back to number 12. Now, the clock says 2 o’clock. If afternoon break ends at 2:15 and
lasts for 15 minutes, then break time starts at 2 o’clock. We counted back from 2:15 to 2
o’clock in five-minute intervals. We could also use a number line to
help us solve the problem. We know that break time ends at
2:15 and lasts for 15 minutes. So, we can start at 2:15 on our
number line and count back in fives. Five, 10, 15 minutes.
Let’s practice finding the start
time when we’re given the duration of an event and the end time.
It is 9 o’clock. Pick the time it was one hour
ago. Was it 8 o’clock, 9 o’clock, or 10
o’clock?
We’re shown two different
clocks. This clock shows 9 o’clock. We have to work out what time it
was one hour ago. So, we need to work out what the
time was an hour before 9 o’clock. The hour before 9 o’clock is 8
o’clock. We know that nine take away one is
eight. So, 9 o’clock take away one hour is
8 o’clock. Which of our three clocks shows
this? It’s the first clock. If it’s 9 o’clock now, then the
time one hour ago was 8 o’clock.
It is 35 minutes after nine. Pick the time it was 15 minutes
ago. Was it 9:20, 9:15, or 9:50?
We’re shown two different
clocks. The second clock shows the end time
after 15 minutes have passed. But we don’t know the start
time. We know that it’s 9:35 after 15
minutes have passed. So, to find the time 15 minutes
ago, we need to count back from 9:35 15 minutes. If we count back five minutes, the
time will be 9:30. And we count back another five
minutes; it’s 9:25. We’ve counted back 10 minutes so
far. And if we count another five
minutes, we’ve counted back 15 minutes altogether. And the time on the clock now says
9:20. We know that 35 take away 15 is
20. So, 35 minutes take away 15 minutes
is 20 minutes.
Which of our three clocks shows the
time 9:20? If it’s 35 minutes after nine, the
time 15 minutes ago was 9:20. To find the answer, we counted back
three lots of five minutes because three fives are 15. The time 15 minutes ago was
9:20.
Mason wants to meet his friends at
the park at 4 o’clock. It will take him 15 minutes to walk
there. What time does he need to leave his
house?
We know that Mason needs to be at
the park at 4 o’clock, and we know it takes him 15 minutes to walk there. We could use a number line to help
us solve this problem. We know that Mason needs to be at
the park by 4 o’clock. Let’s call this the end time. We also know that his walk will
take him 15 minutes. So, we need to use the number line
to find out what time it was 15 minutes ago. We need to count back 15
minutes.
We know that halfway between 3 and
4 o’clock, it’s 3:30. Halfway between 3:00 and 3:30 is
3:15. And halfway between 3:30 and 4
o’clock, it’s 3:45 or quarter to four. So, let’s start at 4 o’clock and
count back 15 minutes. Each of the smaller divisions on
our number line is worth five minutes. If we count back five minutes, that
will take us to 3:55 or five minutes to 4 o’clock. There are 60 minutes in an
hour. So, if we take away five minutes,
we’re at 3:55. If we count back five minutes from
3:55, that will take us to 3:50. Five minutes less than 3:50 is
3:45. So, Mason needs to leave his house
at 3:45.
We can check our answer using a
model of a clock. The minute hand started at number
12, and we had to count back 15 minutes or three lots of five: five, 10, 15. So, if Mason needs to meet his
friends at 4 o’clock and it takes him 15 minutes to walk to the park, he will need
to leave his house at 3:45.
What have we learned in this
video? We have learned how to count in
fives on a clock or a number line to find the duration of events in minutes.
