Ratios, Rates and Proportions ā Digital SAT SAT Math revision notes
A 3-page visual revision sheet for Ratios, Rates and Proportions, 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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Ratios, Rates and Proportions in one look
one relationship held constant while the numbers are scaled up and down
What makes a relationship proportional
two quantities are proportional when their ratio never changes. Triple one and the other triples too
every proportional relationship can be written y=kx, where k is the constant of proportionality, the amount of y that goes with one unit of x
a RATE is a ratio with different units on top and bottom: pages per minute, rupees per litre, people per square kilometre
a UNIT rate is that ratio rewritten with 1 in the denominator, which is what makes it easy to scale to any other amount
Three ways to write the same thing
the equation form, k constanty=kx
the constant read off any one pairk=y/x
the proportion form, then cross multiplya/b=c/dā ad=bc
Worked: a constant rate
Q. a machine fills 84 bottles in 6 minutes. At the same rate, how many bottles does it fill in 15 minutes?
unit rate first: 84/6=14 bottles per minute
scale to the time asked for: 14Ć15=210
or scale the whole block instead: 15 minutes is 2.5 times 6 minutes, so 2.5Ć84=210
Answer: 210 bottles
The three shapes this topic comes in
Rate: an amount per one unit of something else. Find the unit rate, then multiply
Proportion: two ratios set equal with one unknown. Cross multiply and divide
Scale: a drawing, map or similar figure. Every matching length shares one scale factor
Sharing: a total split in a given ratio. Add the parts, divide the total by that
Page 1 of 3. The full sheet, all 3 pages, opens free in the app.
What this Ratios, Rates and Proportions sheet covers
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 Ratios, Rates and Proportions the sheet opens inside the study block itself ā 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.