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In Psychology 101, the ratio of the number of girls to the number of boys is 3:2. After seven more girls join the class, and two boys drop the class, the ratio of the number of girls to the number of boys becomes 5:2. How many students are in the class after these changes?

 Apr 9, 2020
 #1
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the answer is 43!! i just took this course. 

 Apr 9, 2020
 #2
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that is wrong.

peepeepuupuu  Apr 9, 2020
 #3
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ah. sorry about that! i think i made a careless mistake :(( (even tho, of course i care! :))

 

initially,
g = number of girls;
b = number of boys.
Because the ratio of girls to boys is 3:1, therefore
g = 3b                 (1)

finally, we have
g-1 girls because one girl dropped the class;
b+3 boys because three more boys signed up.
Because the new ratio of girls to boys is 5:2, therefore
(g - 1)/(b + 3) = 5/2
Cross multiply.
2(g - 1) = 5(b + 3)
2g - 2 = 5b + 15
2g - 5b = 17            (2)

Substitute (1) into (2) to obtain
2(3b) - 5b = 17
b = 17
g = 3b = 3*17 = 51

Final number of students in the class = 17 + 51 = 68

matthewmacdell  Apr 9, 2020
 #4
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G/B =3/2, 

(G+7)/(B - 2)= 5/2, solve for G, B

 

G = 18 girls  and   B = 12 boys

For a total of 18 + 12 = 30 students.

 Apr 9, 2020

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