Using Simple Formulae
Use simple formulae expressed in words or symbols to calculate values (e.g. perimeter = 2 × (length + width))
What a learner can do afterwards
- Substitute values into P = 2(l + w) to find the perimeter of a rectangle
- Use the formula for area of a triangle (A = 1/2 × b × h) given base and height values
- Interpret a formula expressed in words and use it to compute an output
The lesson
A formula is a short rule that tells you how to work out a value. It uses letters to stand for numbers you don't know yet. Perimeter = 2 x (length + width) is a formula. To use it, you swap each letter for a real number, then work out the answer.
A rectangle has a length of 7 cm and a width of 3 cm. Using P = 2 x (l + w), put the numbers in: P = 2 x (7 + 3). Add first: 7 + 3 = 10. Then multiply: 2 x 10 = 20. The perimeter is 20 cm.
A triangle has a base of 8 cm and a height of 5 cm. The formula is A = 1/2 x b x h. Put the numbers in: A = 1/2 x 8 x 5. Multiply 8 x 5 = 40 first, then take half: 40 divided by 2 = 20. The area is 20 square cm.
Some formulae are written in words, like 'cost = number of tickets x price per ticket.' Read the words carefully, turn them into a calculation, then work it out in the right order: brackets first, then multiplication.
A formula is a rule with letters for numbers. Substitute the numbers in, then calculate step by step in the right order.
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Where it sits
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Where this leads
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8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.