A cyclopentane ring carries a single substituent, the group -CH2-CH(CH3)-CH3. According to the 2013 IUPAC recommendations the ring is the parent hydride. What is the name of the compound?

The substituent chain is numbered from the carbon attached to the ring, which is C1. The methyl group is on C2 of a three-carbon chain, so it is a 2-methylpropyl group. A 1-methylpropyl group would be sec-butyl, and 1,1-dimethylethyl would be tert-butyl. The name is (2-methylpropyl)cyclopentane.