Profit that rohit got by selling 25 pens only is 1×25=25 rs.
but he earns only 5 rupees.that means, he lost 20 rupees by selling pensils.
lost of one pencil is 50 paisa.for one rupee lost, rohit sell 2 pensils.for 20 rupees lost , rohit sells 20×2=40 pencils.