The post-lunch dip is the drop inmental alertness after a midday meal. Does an extract of the leaves of the ginkgo tree reduce the post-lunch dip? Assign healthy people aged 18 to 40 to take either ginkgo extract or a placebo pill. After lunch, ask them to read seven pages of random letters and place an X over eevry e. Count the number of misses per line read. Here are summaries of performance after 13 weeks of either ginkgo extract or placebo: Group Group Size Mean Std Dev.

GINKGO 21 0.06383 0.01462

PLACEBO 18 0.05342 0.01549

a) State hypotheses in terms of the population means for ginkgo and placebo

b) Find the two-sample t statistic

c) Find the P-value. DO these data show that there is a significant effect of ginkgo extract?