Cleo paid monthly rents of $800, $820, $825, $810, and $825 over the last five years. What is the interquartile range (IQR) of her rents?

Order the rents from least to greatest: $800, $810, $820, $825, $825. The lower half is $800 and $810, so Q1 is their average, $805; the upper half is $825 and $825, so Q3 is $825. The IQR is Q3 − Q1 = $825 − $805 = $20, so the correct choice is $20 (C).

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