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Units, Rates and Conversions — Digital SAT SAT Math revision notes

A 3-page visual revision sheet for Units, Rates and Conversions, written for Digital SAT SAT Math. Formulas, diagrams and the traps that cost marks, laid out to be read the night before rather than the term before. Free, and it opens inside CapCompass.

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Units, Rates and Conversions in one look

multiply by one, written as a fraction, until the units you do not want cancel

A unit is part of the answer

  • every conversion factor is a fraction worth exactly 1, because its top and bottom are the same amount written two ways: 60 minutes over 1 hour
  • multiplying by 1 changes the number and never the quantity, which is why a conversion chain can be as long as it needs to be
  • write each factor so the unit you want to LOSE sits diagonally opposite itself, once on top and once underneath. It then cancels
  • a rate carries two units, one over the other. Reading kilometres per hour as a single fraction is what makes it convertible at all

The shapes that keep coming back

  • speed, distance and time v=d/t
  • density of a material ρ=m/V
  • population density, people per unit area D=N/A
  • a conversion factor, worth 1 1=60 minutes/1 hour

Worked: a rate across a unit boundary

Q. a tap runs at 18 litres per minute. How many litres does it deliver in 2.5 hours?

  1. the rate is per MINUTE and the time is in HOURS, so one of them has to move
  2. convert the time: 2.5×60=150 minutes
  3. now the units match: 150×18=2700
  4. check the unit of the answer: minutes times litres per minute leaves litres, which is what was asked for

Answer: 2700 litres

Four rates, one idea

  • Speed: distance per unit time, so kilometres per hour or metres per second
  • Density: mass per unit volume, so grams per cubic centimetre
  • Population density: people per unit area, so people per square kilometre
  • Unit price: cost per unit amount, so rupees per litre or per kilogram

Page 1 of 3. The full sheet, all 3 pages, opens free in the app.

What this Units, Rates and Conversions sheet covers

Open the full Units, Rates and Conversions sheet →Free, works offline, no account needed. All 3 pages, plus a study plan built around your own exam dates.

How CapCompass uses this sheet

These notes are not a standalone PDF. CapCompass plans SAT Math chapter by chapter against your real exam dates and free hours, and when the plan reaches Units, Rates and Conversions the sheet opens inside the study block itself — at the page covering the sub-topic that block is on, with the timer still running. Revision arrives at the moment the plan says revise, instead of having to be gone looking for.

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