Calculate step by step: one-tenth of 400 is 40, one-quarter of 40 is 10, and one-half of 10 is 5. Working backwards through the fractional operations: 400 ÷ 10 = 40, then 40 ÷ 4 = 10, then 10 ÷ 2 = 5. Options 2, 8, 10, and 40 are incorrect results of miscalculating the order or operations.