To determine how many periods of REM sleep Georgia had during her sleep, we need to find out how many 45-minute intervals fit into the total sleep time of 390 minutes.
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Convert her total sleep time into intervals of 45 minutes:
\[ \text{Number of 45-minute intervals} = \frac{\text{Total sleep time}}{\text{Interval length}} = \frac{390 \text{ minutes}}{45 \text{ minutes}} \]
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Performing the division:
\[ \frac{390}{45} = 8.66667 \]
This result means that Georgia experienced 8 full periods of REM sleep, rounding down because you can't have a fraction of a period.
Thus, the total number of periods of REM sleep Georgia had is 8 periods.