What the numbers in a rule mean, step by step
y = −20x + 300 gives the litres in a tank after x minutes.
The question
y = 12x + 60 gives cost in dollars of x tickets. What is the booking fee?
What does the rule start at?
x=0
y = 12 × 0 + 60=60
60
- The start of the story is x = 0 — before any tickets have passed.
- Put 0 in for x: 12 × 0 is 0, so the whole first term disappears and only 60 is left.
- So the number added on the end is always where the story begins. Here that is 60.
How it works.
- 01
The start of the story is x = 0 — before any tickets have passed.
- 02
Put 0 in for x: 12 × 0 is 0, so the whole first term disappears and only 60 is left.
- 03
So the number added on the end is always where the story begins. Here that is 60.