A snack stall sold 250 plates of sandwiches and 150 plates of wraps one morning. The next morning its sandwich sales rose by 20% while its wrap sales fell by 20%. What per cent of the next morning's total plates were sandwiches?

Next morning: sandwiches = $250\times 1.20=300$ and wraps = $150\times 0.80=120$, a total of 420 plates. Sandwiches' share = 300/420 = 0.7143 = 71.43%. 62.5% is 250/400, the first morning's sandwich share, which ignores both changes. 75% is 300/400, the new sandwich count set against the OLD total - the base must move too. 70% comes from assuming the two 20% moves cancel and leave the total at 400; they do not, because the stall sells more sandwiches than wraps.