There are 9 keys on a keychain, of which 5 are for exterior locks and 4 are for interior locks. How many possible selections of 5 keys from the keychain contain at least one key for an exterior lock and at least one key for an interior lock?
There are 9 keys on a keychain, of which 5 are for exterior locks and 4 are for interior locks. How many possible selections of 5 keys from the keychain contain at least one key for an exterior lock and at least one key for an interior lock?