## Graphs Comparing Quantities FAQ

1. Why do I need to be able to substitute in algebra?

Many jobs, such as engineering or those in science and research use formulae to make calculations.

For example, to change temperatures in degrees centigrade (used in Australia and New Zealand) to degrees fahrenheit (used in the US) the formula F = 9C/ 5 + 32 is used.

So if we wish to find the equivalent of 100oC (the boiling point of water) in degrees fahrenheit, we substitute 100 for C in the formula:

F = 9 × 100 / 5 + 32 = 212

So 100oC = 212oF

2. When working out the value of an expression using a substitution does the BEDMAS rule apply?

Yes, the BEDMAS rule for the order that you do operations applies to all mathematics.

3. What are common mistakes made when substituting?

People forget that the BEDMAS rule for the order that you do operations applies toall mathematics.

Example: When substituting into a term like 5p2 there are two ways to try ot work this out. One is very wrong!

 Substitution Calculation Answer Correct or Incorrect? Evaluate 5p2 when p = 3 5 × (3 × 3) 45 CORRECT (5 × 3)2 225 INCORRECT