A 20% fall in the price of rice lets a family buy 4 kg more rice for the ₹800 they spend on it every month. The reduced price per kg (in ₹) is:

At the old price $p$, ₹800 buys $800/p$ kg; at $0.8p$ it buys $1000/p$ kg. The extra $200/p$ kg equals 4, so $p$ = ₹50 and the reduced price is $0.8\times 50$ = ₹40. ₹50 is the OLD price — the question asks for the new one; and ₹32 comes from cutting the ₹40 by a further 20%.