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# Line of Best Fit

 Adding a line-of-best-fit in Excel Use the equation of the line-of-best-fit to predict 'y' values from a 'x' value Use the equation of the line-of-best-fit to predict 'x' values from a 'y' value

A line can be drawn to ‘fit’ the relationship

Using Excel – right click on a data point and 'Add Trend line' and tick the ‘show equation’ box near the bottom

##### The equation line can then be used to predict ‘y’ and ‘x’ values

Eg
If Variable ‘A’ = 10, predict a value for ‘B’

y = 1.026x - 0.3249

so  B = 1.026×10 - 0.3249 = 9.9351  which should be rounded sensibly

B = 9.9 and remember units

##### Predicting ‘x’ from a given ‘y’ is involves solving an equation.

Eg If Variable ‘B’ = 14, predict a value for ‘A’

y = 1.026x - 0.3249

so  14 = 1.026×A - 0.3249

14.3249 = 1.026×A

13.96189 = A

Round sensibly  A = 14

Check the if the solution matches the graph

##### Examples

1) If a student had a Maths score of 14, predict their English Score.

2) If a student had a Maths score of 6, predict their English Score.

3) If a student had a English score of 8, predict their Maths Score.

4) If a student had a English score of 16, predict their Maths Score.

5) How accurate are these predictions?