Turn a rule in words or a diagram into a formula, keep the units straight, then use it.
What you will learn
- Write a formula from words
- Write a formula from a diagram
- Use a formula you have written
From words to a formula
"Mugs cost £8 each plus £4 delivery for the order": n mugs cost 8n, and the delivery is added once, so C = 8n + 4.
Check with a number: 3 mugs should cost £28, and 8 × 3 + 4 = 28.
Keep the units the same: £3 plus 45p a minute, in pounds, is C = 3 + 0.45m.
A starting amount plus a fixed amount for each step: a box holds 5 pens and each pack added holds 4 more, so N = 5 + 4p. With p = 6 packs, N = 5 + 24 = 29. In the same way, "her dad is 5 years more than 2 times Ella's age x" gives y = 2x + 5, and "roast for 40 minutes per kilogram plus 20 minutes" gives T = 40w + 20.
The rest of this lesson and its 7 practice questions are locked.
In this lesson
- From words to a formula
- From a diagram
7 practice questions, marked as you go; about 20 minutes in all.
In this unit: Formulae and rearranging
Substitute into formulae, write your own, change the subject (including when it appears twice) and use rearranged formulae from science and finance.