A relief fund of ₹8,40,000 was used as follows: 35% on food packets, 25% on medicines and ₹1,68,000 on shelter. What per cent of the fund was left unused?

Shelter took 168000/840000 = 0.20, that is 20% of the fund, so the three heads together used 35 + 25 + 20 = 80%, leaving 100 - 80 = 20% unused. 40% is 100 - 60, which forgets the shelter spending entirely. 80% is the share used rather than the share left, and 45% drops the medicines head.