Mental Math · Percent Sense
Every percent is just a few clean slices carved off one bar — try each one in your head first, then watch the trick that makes it easy.
1 Explore — try these first
Try before you watch. Pick a level below and give the problem an honest try on paper first — wrong turns and all. Then open the video to see the trick. Every level rides one habit: Every percent is built from the seven anchors — 1, 5, 10, 20, 25, 50, 75% — once you can carve those slices off a bar, every other percent is just slices added, scaled, or subtracted.
★ · Carve the Bar
What is 25% of 240? And what is 75% of 80?
L0 · All Seven Anchors
What is 5% of 80? And what is 20% of 250?
L1 · Scale the Anchor
What is 7.5% of 56? And what is 175% of 32?
L2 · Stack & Unstack Anchors
What is 15% of 240? And what is 65% of 160?
L3 · Divide Then Multiply
What is 66 2/3% of 72? And what is 87.5% of 96?
L4 · A Percent of a Percent
What is 12% of 200? And what is 22.5% of 160?
L5 · Lean on the Whole
What is 96% of 50? And what is 104% of 50? A $120 game has 13% tax added — what is the final price? And a $1,000 card goes up 10%, then down 10% — is it back to $1,000?
L6 · Swap to the Anchor
What is 84% of 25?
2 Learn — watch the solutions
Gave each one a real try? Now watch the trick. (Stuck is fine — that's the point.)
★ · Carve the Bar
Peek the trick — Carve the Bar
Draw the whole as one bar and carve off the slice the percent names — 10% means ÷10, 1% means ÷100, 50% means ÷2, 25% means ÷4 — and for 75% you quarter the bar and take THREE of those slices: 75% = 3 × (N ÷ 4), never 'just ÷4'.
L0 · All Seven Anchors
Peek the trick — All Seven Anchors
If you must take a percent, recognize which of the seven anchors it is — 1% = ÷100, 5% = half of 10%, 10% = ÷10, 20% = ÷5, 25% = ÷4, 50% = ÷2, 75% = 3 × (N ÷ 4) — and carve that one slice off the bar.
L1 · Scale the Anchor
Peek the trick — Scale the Anchor
If a percent is a relative of an anchor — a tenth of it (p/10), or 100% plus it, or 100% minus it — compute the anchor first by the carve you already know, THEN scale: ÷10 the result, add it to N, or subtract it from N. Anchor first, then scale — never invent new arithmetic.
L2 · Stack & Unstack Anchors
Peek the trick — Stack & Unstack Anchors
If a percent isn't an anchor, BUILD it from anchors — stack slices to reach it (15% = 10% + 5%, 65% = 50% + 10% + 5%) or carve one anchor and shave a smaller one off (45% = 50% − 5%, 40% = 50% − 10%) — then add or subtract the slice values. For scaled or over-100% cousins, build the combined base first, then ÷10 or ± N.
L3 · Divide Then Multiply
Peek the trick — Divide Then Multiply
If a percent is a friendly fraction — thirds (33⅓% = ⅓, 66⅔% = ⅔), sixths (16⅔% = ⅙, 83⅓% = ⅚), or eighths (12.5% = ⅛, 37.5% = ⅜, 62.5% = ⅝, 87.5% = ⅞) — divide N by the denominator first, then multiply by the numerator: carve the bar into that many equal slices, take the numerator's worth.
L4 · A Percent of a Percent
Peek the trick — A Percent of a Percent
If the percent isn't an anchor but sits right beside one (11, 12, 13, 15 hug 10%; 22.5, 27.5, 37.5 hug 25%), carve the nearby anchor slice off the bar FIRST, then carve a small fraction OF THAT SLICE and add it on (or shave it off) — the inner fraction always acts on the anchor slice, never on the whole bar.
L5 · Lean on the Whole
Peek the trick — Lean on the Whole
If a percent is near 100%, carve the small missing slice (1% = N ÷ 100) and subtract from N; if it's just over 100%, read it as 200% minus its complement (104% = 200% − 96%) — then chain one applied factor for the final amount.
L6 · Swap to the Anchor
Peek the trick — Swap to the Anchor
a% of b = b% of a (because ab/100 = ba/100). When one number is a friendly anchor you already own, swap so THAT number becomes the percent, then carve or lean the other number — the scary head-on grind becomes a quarter cut.
3 Master — practice on your own
Print the practice sheet and solve without the videos. Check your answers at the back — if one is wrong, the answer key names the trick so you know exactly which video to rewatch.
Download fresh practice problems PDF
