H0:μ1−μ2 ≥ 2
H1:μ1−μ2 <2
α = 0.01 RR={ t < -t0.01(14)=-2.624}
t.s.: t= (X1-X2)-(μ1−μ2) / √[SP2/n1 + SP2/n2] = (10-10)-2 / √[4/7 + 4/9] = -1.984 → not Re H0
結論:沒有證據顯示μ1−μ2 <2