A council records the age x x\,x years and annual repair cost y y\,y pounds for a self-contained random sample of 40 buses. The regression line of y y\,y on x x\,x is y=315x+740y=315x+740y=315x+740. One bus is 8 years old and has an annual repair cost of £3900.
Find the predicted repair cost for this bus.
Find its residual.
Explain why the regression line alone cannot establish that age causes higher repair costs.
178 exam-style questions on WJEC A Level Maths 4.3.1 Statistical hypothesis testing (A-level only). Each one has a worked solution and a mark scheme showing where the marks go.