30% of 400 is 120. Decimals give the same story: 0.30 × 400 = 120. Because four hundred is 4 × 100, you can read thirty percent as “thirty from each hundred”: 30 + 30 + 30 + 30 = 120. The tenth shortcut is equally smooth: 400 ÷ 10 = 40, then 40 × 3 = 120. On this base, 25% of 400 is 100 and 20% of 400 is 80; stepping up by one 10% of 400 (40) takes you from eighty to one-twenty. Alternatively, 25% + 5% is 100 + 20 = 120, since 5% of 400 = 20.
A 30% off £400 sticker means £120 off and you would usually pay £280 before extras. If the wording asks for thirty percent of four hundred, the answer is 120, not the post-discount total.
Same rate on nearby totals: 30% of 300 is 90, so adding a hundred to the base adds 30 to the slice at this percentage (90 + 30 = 120). 30% of 500 is 150, another 30 per extra hundred. 30% of 320 is 96; moving the base up by eighty lifts the thirty-percent share by 24 (96 + 24 = 120), which matches 30% of 80.
Magnitude trap: 30% of 4000 = 1200. Dropping a zero from the base but not from the answer is how 120 and 1200 get confused in quick estimates.
If £400 is reduced by 30%, the reduction is £120 and you pay £280 (before other charges).
Change either value below to solve another percentage-of-number question instantly.
Formula used: (percentage ÷ 100) × number
Step 1: Convert 30% → 0.30 (divide 30 by 100).
Step 2: Multiply: 0.30 × 400 = 120.
Full formula: (30 ÷ 100) × 400 = 120
Tenths: 10% of 400 = 40; 40 × 3 = 120. Or sum four lots of 30 (thirty percent of each hundred).
The base is a multiple of both 100 and 10, so “per hundred” thinking and “one tenth” thinking stay integer-clean: no stray halves unless you change the percentage. That is why worksheets and pricing examples often use four hundred when they want a neat thirty-percent slice.
After you remove thirty percent, 70% remains: 400 − 120 = 280, or 0.70 × 400 = 280. Pairing 120 with 280 is the familiar discount layout—saving versus amount still due—on a simple model.
Half of four hundred is 200; thirty percent of that half is 60, and doubling back checks out as 120 on the full amount if you reason from “half the total” first.
Fastest for many people: one tenth is 40; triple it → 120.
15% of 400 is 60; doubling that percentage lands on 120 as well.
50% of 400 is 200; thirty percent is three-fifths of that half—more work mentally than tripling forty, but valid as a cross-check.
Example 1: Thirty percent off a £400 laptop
The saving is £120 and you pay £280 if nothing else applies.
Example 2: Retainer on a £400 invoice
A 30% upfront slice is £120; the rough “still to bill before extras” figure is £280 on a strict split.
Example 3: Time
30% of a 400-minute day chunk is 120 minutes—two hours of the block.
Example 4: Tenfold slip
On 4000, 30% is 1200. One wrong zero turns 120 into 1200.
30% of 400 is 120.
Find 10% of 400 (40) and multiply by 3, or add 30% of each of the four hundreds (30 × 4), or compute 0.30 × 400.
Removing the 30% portion (120) from 400 leaves 280.
Because 10% of 400 is 40 with no fraction, and 30% is three times that tenth; also 400 is four hundreds and 30% of each hundred is 30.