The mean of marks secured by 30 students in division-A of class X is 67, 55 students of division-B is 63 and that of 40 students of division-C is 61. What is the mean of marks of the students of three divisions of Class X?
Total marks secured by 35 students in division A = 30 $$\times$$ 67 = 2010
Total marks secured by 45 students in division B = 55 $$\times$$ 63 = 3465
Total marks secured by 70 students in division C = 40 $$\times$$ 61 = 2440
=> Mean of marks of the students of three divisions of Class X = $$\frac{(2010 + 3465 + 2440)}{(30 + 55 + 40)}$$
= $$\frac{7915}{125} = 63.32$$
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