CalcAnyway · Examples
Examples
"How would you build this calculation?", answered with a board you can actually move.
Every article has a working CalcAnyway board embedded in it. You can change the numbers as you read and check what the text says.
Changes made in the page are not saved. To carry on with your own numbers, press "Open in CalcAnyway" first and edit there — that copy can be saved and shared as a URL.
Categories
Study
Fractions, area, rounding, units, data, concentration, levers, circuits — the places that are easy to get wrong.
Money
Prices, costs and percentages. Most money examples are Japan-specific and in Japanese; the page links to them.
Latest
Compound interest — the future value from an annual rate and a number of years
Money — The future value from the principal, the rate and the years. In this example, 100 at 5% for 10 years is about 162.89, not the 150 from adding 5 a year.
Compound annual growth rate (CAGR) — the yearly rate from a start value and an end value
Money — The steady yearly rate from a start value, an end value and the years. In this example, 100 to 150 in five years is about 8.45%, not 10%.
Margin and markup — how they differ and how to calculate each
Money — Margin is gross profit ÷ price, markup is gross profit ÷ cost. Here cost 80 and price 100 give 20% and 25%; a 20% target gives prices of 100 and 96.
Percentage change — the new value, and the rise needed to get back
Study — 1,000 to 800 is −20%. A 20% rise from 800 only reaches 960; getting back to 1,000 takes 25%.
Division and fractions — quotient and remainder, fraction, decimal
Study — 13 ÷ 4 is 3 remainder 1, 3 1/4 or 3.25. Why the three forms match, and why the remainder is smaller than the divisor.
Rounding — to the nearest, up and down
Study — 34,567 to the thousands: 35,000 to the nearest or rounded up, 34,000 rounded down. The hundreds digit decides.
Area of a triangle — why it is base × height ÷ 2
Study — A triangle with base 6 and height 4 is 6 × 4 ÷ 2 = 12: exactly half of the parallelogram (24) with the same base and height.
Unit conversion — length, area and time
Study — 350 cm is 3.5 m, 1 m² is 10,000 cm², and 142 minutes is 2 h 22 min (about 2.37 hours) — with the reason behind each factor.
Mean and median — how they differ and how to find each
Study — Eight scores: mean 78.25, median 81. With one score changed to 0, the mean drops to 70.5 and the median stays at 81.
Scaling a recipe — the factor from servings or from an ingredient
Study — A recipe for 4 cooked for 6 is ×1.5: 400 g of meat becomes 600 g. Also the factor from the meat you have, and why one factor keeps the ingredients in the same proportions.
Average speed for a round trip — total distance over total time
Study — Total distance ÷ total time. 60 km/h out and 30 km/h back gives 40 km/h, not the 45 km/h from averaging the two speeds.
Concentration — finding it, diluting and mixing
Study — 20 g of salt in 180 g of water is 10%: the divisor is the whole solution, not the water. Also the water to add when diluting, and how much of two solutions to mix.
Balancing a lever — weight times distance from the pivot
Study — Weight × distance from the pivot has to match on both sides: 60 g at 20 cm balances 40 g at 30 cm. Also several weights on one side, and the force to lift a load with a bar.
Resistors in parallel — the combined resistance from the branch currents
Study — Add the branch currents, then divide the voltage by the total. 4 Ω and 6 Ω in parallel across 12 V draw 5 A, so the combined resistance is 2.4 Ω.