Formula Calculator

Pre-Algebra · Axiom Academy

LESSON Plugging Numbers Into Formulas A formula is a recipe — substitute real measurements for the variables and it evaluates to a real quantity. Take a rectangle that is 10 ft long and 6 ft wide. The area formula doesn't care about these particular numbers — it works for any length and width. To use it, substitute : drop the measured numbers into the variables' slots, then multiply. Substitute the measurements, then multiply 2. Different Formulas, Same Move Every formula behaves like a little machine : numbers go in the top, the rule processes them, an answer comes out the bottom. The variables change, but the move is always the same — substitute, then compute. Here are three more, each fed a real value. P = 2(L + W) . With L=10 , W=6 : P = 2(10+6) = 32 ft of border. . With P= 1000 , r=0.05 , t=3 : I = 1000 0.05 3 = 150 , i.e. 150 in interest. Read the formula, slot in each measured value, do the arithmetic. The units of the answer follow from the formula. Heating something to 68°F ? Feed 68 into the temperature machine: , so that's 20°C . Same machine, any input — give it 212°F and it returns 100°C, the boiling point of water. When you substitute, you carry the units in with the number — and that's not decoration. The bare number 10 tells you almost nothing on its own. Attach a unit and it snaps into meaning: a length, a price, a temperature.

This is the written version of the interactive lesson above. See the full Pre-Algebra course.