Count back in 10s from 90 to find 90 − 30.
Count back in tens from 90 to find 90 take away 30.
We need to start at 90 and count back 10: 80. Now we need to count back 10 from 80, which is 70.
Since 30 is three tens, we’ve already counted back two tens. We need to count back one more 10: 60. 90 take away 30 is 60.
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