Video Transcript
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.