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# I have no idea how to do this question

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7 There are 10 boys and 20 girls in a class. The class has a test. The mean mark for all the class is 60 The mean mark for the girls is 54 Work out the mean mark for the boys

Oct 14, 2018

#1
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$$total_{all} = (n_{boys}+n_{girls})m_{total} = (10+20)60 = 1800 \\ total_{girls} = n_{girls}m_{girls} = 20 \times 54 = 1080 \\ total_{boys} = total_{all}-total_{girls} = 1800 - 1080 = 720\\ m_{boys} = \dfrac{total_{boys}}{n_{boys}}= \dfrac{720}{10}=72$$

kind of a sexist problem :P

Oct 14, 2018

#1
+4490
+2

$$total_{all} = (n_{boys}+n_{girls})m_{total} = (10+20)60 = 1800 \\ total_{girls} = n_{girls}m_{girls} = 20 \times 54 = 1080 \\ total_{boys} = total_{all}-total_{girls} = 1800 - 1080 = 720\\ m_{boys} = \dfrac{total_{boys}}{n_{boys}}= \dfrac{720}{10}=72$$

kind of a sexist problem :P

Rom Oct 14, 2018
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