Rearranging formulae

Mathematics · Algebra · ages 12-14

Name ______________________ Date ____________

In the formula A = l x w, what is the subject?
- A
- l
- w
Rearrange C = 2πr to make r the subject.
- r = C - 2π
- r = 2π - C
- r = C / (2π)
- r = 2πC
Use the formula P = 4s with s = 6. What is P?
Answer: ______________
In the formula v = d ÷ t, what is the subject?
- v
- d
- t
Make x the subject of y = (x + 3) / 2.
- x = 2y - 3
- x = y / 2 - 3
- x = 2y + 3
- x = (y - 3) / 2
The formula for speed is v = d ÷ t. Rearrange it to make d the subject, then find d when v = 20 and t = 4.
Answer: ______________
Rearrange y = 3x + 5 to make x the subject, then find x when y = 20.
Answer: ______________
Rearrange y = x + 5 to make x the subject.
- x = y + 5
- x = 5 - y
- x = y - 5
Rearrange A = πr² to make r the subject.
- r = (A ÷ π)²
- r = √(A ÷ π)
- r = A ÷ π
The formula F = 9C / 5 + 32 converts Celsius to Fahrenheit. What is F when C = 20?
Answer: ______________

Answer key

For grown-ups. Fold this page away before handing over the rest.

A · A is alone on the left of the equals sign, so A is the subject.
r = C / (2π) · Divide both sides by 2π: r = C / (2π).
24 · Substitute s = 6: P = 4 x 6 = 24.
v · The subject is the letter standing alone on one side. Here that's v.
x = 2y - 3 · Multiply by 2 then subtract 3: x = 2y - 3.
80 · d = v x t, so d = 20 x 4 = 80.
5 · x = (y - 5) / 3, so x = (20 - 5) / 3 = 5.
x = y - 5 · Subtract 5 from both sides to undo the addition: x = y - 5.
r = √(A ÷ π) · Divide both sides by π first, then take the square root to undo the squaring.
68 · F = 9 x 20 / 5 + 32 = 36 + 32 = 68.