At a research centre, a trial is conducted to see if a new fertiliser gives a better yield of potatoes than the usual fertiliser. Ten plots of land are available for the trial. Each plot is spilt into two equal halves: one half is treated with the new fertiliser, the other half with the usual fertiliser. The following table gives the yield, in kg, per half plot.

Using a sign test, at the 5% significance level, investigate whether the new fertilizer produces an increased average yield.

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Plot 3 8. 10 Usual 20.2 22.0 17.8 20.6 26.8 20.9 21.2 16.5 20.8 12.9 New 20.8 24.3 17.0 21.2 27.7 19.4 22.6 17.3 20.9 13.1