# Question Video: Using Place Value Strategies to Subtract within 100 Mathematics • 1st Grade

We can count back by ones and tens to find the difference. We can use base ten blocks to help us. Use this strategy to find the difference using the blocks: 78 − 5. Find the difference: 78 − 50.

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### Video Transcript

We can count back by ones and tens to find the difference. We can use base ten blocks to help us.

To find 46 take away four, count back by ones. 46 take away four ones equals 42. To find 46 subtract 40, count back by tens. 46 take away 40 or four tens equals six. Use this strategy to find the difference using the blocks.

78 take away five: think! Do you need to count back by ones or tens? We need to calculate 78 take away five, so we’re just taking away five ones: one, two, three, four, five. 78 take away five is 73.

Find the difference: 78 take away 50. Think! Do you need to count back by ones or tens? The five in 50 is worth five tens, so we need to take away or count back five tens: one, two, three, four, five. Now we have two tens and eight ones. The difference between 78 and 50 is 28. We found the difference between 78 and five by taking away the ones, to find the answer of 73, and the difference between 78 and 50 is 28.

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