Read conversion, distance-time and cost graphs, say what the gradient and intercept mean, and solve simultaneous equations where two lines cross.
What you will learn
- Use conversion graphs, including for values off the graph
- Find speed from a distance-time graph
- Interpret the gradient and intercept in context
- Solve simultaneous equations by reading where two lines cross
Gradient is a rate
On a real-life graph the gradient is a rate: the change in the vertical quantity for each one unit across.
On a distance-time graph that rate is the speed.
- out: 10 km in 30 minutes = 10 km in 0.5 hours
- speed = 10 ÷ 0.5 = 20 km/h
- flat part: 30 to 50 minutes, stopped for 20 minutes
- home: 10 km in 40 minutes, 10 ÷ (40/60) = 15 km/h
Convert the minutes to hours before dividing, or the answer comes out in km per minute.
At a steady speed, distance = speed × time: 3 m/s for 40 seconds is 120 m.
The rest of this lesson and its 7 practice questions are locked.
In this lesson
- Gradient is a rate
- The intercept is the starting value
- Where two lines cross
- Try it: Find the crossing point
7 practice questions, marked as you go; about 25 minutes in all.
Key terms
Gradient, Intercept
In this unit: Straight-line graphs
Coordinates and midpoints, gradients and intercepts, the equation of a line, parallel and perpendicular lines, and straight-line graphs in real life.