A unit set itself a monthly target of 4,500 pieces but turned out only 3,825 pieces. The shortfall is what per cent of the target?

The shortfall is 4500 - 3825 = 675, and the words 'of the target' fix 4,500 as the base: 675/4500 = 0.15 = 15%. 17.65% divides by the pieces actually turned out (675/3825) - the wrong base. 85% is 3825/4500, which reports the achievement instead of the shortfall, and 1.5% is a slipped decimal point.