Today is rung 11 of 13 on this topic
Percent in the real world — tax, tip, interest, markup
Can do: Solves multi-step percent problems including successive changes and finding the original amount.
Why it matters
This is the maths of adult life. It's also where the deepest intuition failures live — most adults get successive percentages wrong.
What it looks like when it's wobbly
Adds percentages that shouldn't be added, and can't reverse a percentage change.
⏱️ Two-minute check
"A $80 item, 25% off, then 8% tax. Final price? A jacket cost $60 after 25% off — what was it before?"
Solid looks like: $64.80 and $80.
The full activity for this topic · 25 minutes
Real Receipts
- 1Take a real receipt and verify the tax line yourself.
- 2Work out what a 20% tip would be, mentally first.
- 3Do a two-step problem: sale price then tax, and note the order matters less than people think — check why.
- 4Reverse one: given the final price and the discount, find the original.
- 5Try simple interest on a real savings rate over three years.
If it's too hard
One-step problems with mental 10% anchoring.
If it's too easy
Compound interest over five years, and comparing two loan offers.
Say this
"25% off means you pay 75%. Multiply by 0.75 — one step instead of two."