The data below shows the number of students in class A and B having secured different marks.
What is the combined mean of A and B?
Mean of A = $$\dfrac{1\times3+3\times4+5\times1+7\times1+9\times1+11\times0}{3+4+1+1+1+0} = \dfrac{3+12+5+7+9}{10} = \dfrac{36}{10} = 3.6$$
Mean of B = $$\dfrac{1\times2+3\times1+5\times3+7\times1+9\times1+11\times2}{2+1+3+1+1+2} = \dfrac{2+3+15+7+9+22}{10} = \dfrac{58}{10} = 5.8$$
Combined mean of A and B = $$\dfrac{3.6+5.8}{2} = \dfrac{9.4}{2} = 4.7$$
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