20% of 400 is 80. One fifth of four hundred is eighty: 400 ÷ 5 = 80. Decimals agree: 0.2 × 400 = 80. Because 400 = 300 + 100, add 20% of 300 (60) and 20% of 100 (20): 60 + 20 = 80. 10% of 400 is 40; doubling gives 80 again. 400 = 8 × 50 and 20% of 50 = 10, so eight tens make 80. On the same base, 25% of 400 is 100 and 30% of 400 is 120—so twenty percent is the clean whole-number fifth below those neighbours.
Read 20% off £400 as “remove £80,” leaving £320 before extras. If someone asks for twenty percent of four hundred—fee, slice, or allocation—the answer is 80, not three hundred and twenty. The remainder only matches “after discount” wording.
Compare bases: 20% of 300 is 60 and 20% of 500 is 100, so four hundred’s fifth sits between those at 80. 20% of 350 is 70; adding fifty to the base adds ten to the fifth (70 + 10 = 80). 20% of 200 is 40, so moving from two hundred to four hundred doubles the base and doubles the fifth (40 × 2 = 80).
Multiply the base by ten: 20% of 4000 is 800. If a four-hundred-pound subtotal becomes four thousand on the same percentage rule, the slice scales the same way—watch the decimal so you do not report 80 or 8000 by mistake.
If £400 is reduced by 20%, the reduction is £80 and you pay £320 (before other charges).
Change either value below to solve another percentage-of-number question instantly.
Formula used: (percentage ÷ 100) × number
Step 1: Convert 20% → 0.2.
Step 2: Multiply: 0.2 × 400 = 80.
Full formula: (20 ÷ 100) × 400 = 80
Fifth shortcut: 400 ÷ 5 = 80. Split: 20% of 300 + 20% of 100 = 60 + 20 = 80.
Four hundred is 40 × 10, so 10% = 40 and doubling lands on 80 without leaving the tens pattern.
Against 20% of 100 (20): the base is four times larger, so the fifth is 20 × 4 = 80—a quick structural check whenever you see round hundreds.
Fastest: 400 ÷ 5 = 80.
From 25% of 400 = 100, subtract 5% of 400 = 20 to land on eighty—useful if quarters come first mentally.
Example 1: Twenty percent off a £400 fee
The markdown is £80 and you pay £320 if nothing else stacks.
Example 2: Four-hundred-unit batch
If a 20% quality hold applies, 80 units are ring-fenced and 320 are free to ship under a strict rule.
Example 3: Budget line
Allocating 20% of a £400 sub-budget means £80 for that line and £320 notionally elsewhere—not the other way round unless the wording says “after discount.”
Example 4: Tenfold check
20% of 4000 is 800. If you see 80 or 8000 on the scaled row, revisit the percent-to-decimal step.
20% of 400 is 80.
Multiply 400 by 0.2, divide 400 by 5, or double 10% of 400 (40 → 80).
20% off 400 is a reduction of 80, leaving 320.