Find any quantity in a formula from science or finance: rearrange first, or substitute and solve.
What you will learn
- Find an unknown quantity in a formula
- Use formulae for motion, density, electricity and growth
- Round answers sensibly
Substitute, then solve
If v = u + at and you know v, u and a, put the numbers in and solve for t, or rearrange first and then substitute.
Both give the same answer.
- s = ut + ½at², s = 54, u = 3, t = 6
- 54 = 18 + 18a
- 18a = 36, so a = 2
The same works for an area: a trapezium with parallel sides a and b and height h has A = ½(a + b)h. With A = 30 and parallel sides 7 and 5: 30 = ½ × 12 × h = 6h, so h = 5.
The rest of this lesson and its 7 practice questions are locked.
In this lesson
- Substitute, then solve
- Formulae from other subjects
- Try it: Use the calculator for growth
7 practice questions, marked as you go; about 25 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.