Question

PLEASE TELL ME IF THIS IS CORRECT!!!!!!!! EXPLAIN HOW?

Answer 1

If we have 40 girls in the choir, and 18 of them are in 7th grade while there are 36 7th grade choir members, that means 18 of the 36 7th grade choir members are boys. So there are 18 7th grade boys. So we have to add the 40 girls and the 18 7th grade boys and divide it by 80 to get
`(58)/(80)=(29)/(40) = B`

You are correct.

Answer 2

The General formula for this kind of a problem (or) is

P(Girls or Grade7) = P(Girls) + P(Gr_7) - P(Girls and Grade 7)

P(Girls) = 40/80 Given

P(Gr7) = 36/80 Given

P(G7 and Girls) = 18 / 80 This is also given (sort of) The number of girls is 40 of those 40, 18 of them are in grade 7. So the 18 (for and) are taken over 80, not 40

Substitute

P(girls or Gr7) = 40/80 + 36/80 - 18/80

P(Girls or Gr7) = 76/80 - 18/80

P(Girls or Gr7) = 58 / 80

P(girls or Gr7) = 29/40

All of us are getting B <<<< Answer