Scatter Graphs Finding the equation of the line of best fit GCSE Statistics Scatter Graphs Finding the equation of the line of best fit

Using a line of best fit there are a couple of terms used in the statistics GCSE that are not used in Unit 1 Interpolation – this is when the data point you need lies within the range of the given data values - this gives fairly reasonable estimates Extrapolation – this is when the data point you need is outside the range of given data values - this gives unreliable estimates

Equation of a line of best fit This is the same as the equation of any straight line in that it takes the form y=mx + c Also written (for some reason) y = ax + b Where a (or m) is the gradient change in x change in y b is the value of y when x = 0 (the intercept) if you use a false origin you can not read b from your graph if b can not be read from the graph, put the value of a into the equation and the coordinates of a point on the line, then solve the equation to find b

Interpreting the gradient a and the intercept b the gradient here is 2.4 4.8 =0.5 in context this means the cost for each mile travelled is £0.50 the intercept is £1.85 in context this is the standing charge the taxi driver has

Your turn Exercise 5F page 189