My daugter got this question - i dont agee with the answer the teacher gave

Question

" In a certain class, the ratio of pass grades is 7 to 5. How many of 36 students failed the course?"

Answer 1

5/12 of 36 failed

 

(5/12)36 = 15 failed

 

Answer 2

P = number that passed

 

F = number that failed

 

P/F = 7/5

 

P + F = 36

 

Then

 

P = 36 - F

 

(36 - F)/F = 7/5

 

36 - F = (7/5)F

 

36 = F(7/5 + 1) = F(12/5)

 

F = (5/12)(36) = 15

 

15 failed.

 

P = 36 - F = 36 - 15 = 21

 

21 passed.

 

Test the answers:

 

Is P/F = 7/5 ?

 

P/F = 21/15 = 7/5  [good]

 

Is P + F = 36?

 

P + F = 21 + 15 = 36  [good]