WEBVTT
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It is 35 minutes after nine.
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Pick the time it was 15 minutes ago.
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Was it 9:20, 9:15, or 9:50?
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We’re shown two different clocks.
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The second clock shows the end time after 15 minutes have passed.
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But we don’t know the start time.
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We know that it’s 9:35 after 15 minutes have passed.
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So, to find the time 15 minutes ago, we need to count back from 9:35 15 minutes.
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If we count back five minutes, the time will be 9:30.
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And we count back another five minutes; it’s 9:25.
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We’ve counted back 10 minutes so far.
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And if we count another five minutes, we’ve counted back 15 minutes altogether.
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And the time on the clock now says 9:20.
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We know that 35 take away 15 is 20.
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So, 35 minutes take away 15 minutes is 20 minutes.
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Which of our three clocks shows the time 9:20?
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If it’s 35 minutes after nine, the time 15 minutes ago was 9:20.
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To find the answer, we counted back three lots of five minutes because three fives are 15.
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The time 15 minutes ago was 9:20.