We often use formulas without even noticing. For example, we might convert miles to km by multiplying by 1.6, or find the circumference of a circle by multiplying pi by the diameter.
km = 1.6 x miles is an example of a formula.
Using formulas
We have already seen that km = 1.6 x miles and C = 
× d are examples of formulas. There are many others that we use regularly in other subjects. Sometimes we have to construct our own formula:
Example
A taxi firm charges 50p per mile plus a fixed charge of £2.00. Write down a formula for the cost (C) of hiring this taxi to travel ‘n’ miles.
Solution
- Travelling 1 mile would cost £2 + 50p.
- Travelling 2 miles would cost £2 + 2 x 50p.
- Travelling 3 miles would cost £2 + 3 x 50p.
So travelling for 'n' miles will cost £2 + n x 50p.
The formula is C = £2 + (n x 50p)
- Question
A rectangle has a width of x and a length of 2x.
Write down a formula for the perimeter (P) in terms of x.
- Answer
P = 2x + x + 2x + x
Did you remember to include all 4 sides?
So P= 6x
Links
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