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Everyday Math

Practical formulae for daily life: shopping, cooking, travel, and home projects.

Unit Price

Basic
Unit Price=Total PriceQuantity\text{Unit Price} = \frac{\text{Total Price}}{\text{Quantity}}

Price per single unit to compare value between products.

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Discount Price

Basic
Final=P(1d)\text{Final} = P(1 - d)

Price after a percentage discount.

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Sales Tax Total

Basic
Total=P(1+t)\text{Total} = P(1 + t)

Final price including sales tax.

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Tip Amount

Basic
Tip=B×r\text{Tip} = B \times r

Gratuity based on a bill amount.

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Fuel Economy (mpg)

Basic
mpg=MilesGallons\text{mpg} = \frac{\text{Miles}}{\text{Gallons}}

Distance traveled per gallon of fuel.

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Trip Fuel Cost

Basic
Cost=DE×p\text{Cost} = \frac{D}{E} \times p

Total fuel cost for a trip.

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Average Speed

Basic
v=dtv = \frac{d}{t}

Distance covered per unit time.

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Travel Time

Basic
t=dvt = \frac{d}{v}

Time needed to cover a distance at a given speed.

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Recipe Scaling

Basic
Qnew=Qold×SnewSoldQ_{new} = Q_{old} \times \frac{S_{new}}{S_{old}}

Adjust ingredient quantities for a different number of servings.

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Paint Needed

Basic
Gallons=AC\text{Gallons} = \frac{A}{C}

Amount of paint required for a wall area.

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Tiles Needed

Basic
N=AfloorAtileN = \frac{A_{floor}}{A_{tile}}

Number of tiles to cover a floor.

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Room Area

Basic
A=l×wA = l \times w

Floor area of a rectangular room.

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Simple Interest

Basic
I=PrtI = P r t

Interest earned or owed without compounding.

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Celsius to Fahrenheit

Basic
F=95C+32F = \frac{9}{5}C + 32

Convert temperature from Celsius to Fahrenheit.

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Body Mass Index

Basic
BMI=mh2BMI = \frac{m}{h^2}

Weight-to-height ratio used as a health screening tool.

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Percentage Change

Basic
%Δ=newoldold×100\%\Delta = \frac{new - old}{old}\times 100

Relative change between two values.

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Split the Bill

Basic
Each=T(1+r)n\text{Each} = \frac{T(1+r)}{n}

Per-person share of a bill including tip.

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Monthly Loan Payment

Intermediate
M=Pr(1+r)n(1+r)n1M = P\frac{r(1+r)^n}{(1+r)^n - 1}

Fixed monthly payment for an amortizing loan.

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Weight Loss Estimate

Intermediate
Δw=deficit×days7700\Delta w = \frac{\text{deficit} \times days}{7700}

Approximate body-mass loss from a calorie deficit (kg).

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Aspect Ratio Scaling

Basic
h=w×rhrwh = w \times \frac{r_h}{r_w}

Find a height that preserves an aspect ratio.

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