Question

Plz help its due TOMMOROW​

Answer 1

Answer:

  86%

Step-by-step explanation:

Let g represent the mean mark for the 10 girls in the class. Then the mean mark for the class was ...

  10g +20(62%) = 30(70%)

  g = 3(.7) -2(.62) . . . . . . . . . divide by 10 and subtract 2(.62)

  g = .86 = 86%

The mean mark for girls was 86%.

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You can do this in your head if you consider it in terms of deviations from the mean. The second equation above can be rewritten and factored as ...

  g = 70% +2(70% -62%)

That is, because there are 2 boys for every girl, the girl's score is above the mean by an amount that is 2 times the amount that the boy's score is below the mean. The boys' score is below by 8%, so the girls' score is above by 16%, so is 86%.