That's what I thought, too.
If the reason for an "OutputPeripherals" class was to have multiple instances that could each output a 'number' the pointer in the InputPeripherals class should point to an instance of OutputPeripherals. Then the InputPeripherals instance could call myOutputPeripheral->number(value); to display the number 'value' on the selected output peripheral.
Then with a LEDOutputPeripheral class could be a derived class of OutputPeripherals.