Academy 23151

There are 180 pupils in the 1st year of the academy. There are seven girls for every five boys. How many girls are there in the year?

Correct answer:

d =  105

Step-by-step explanation:


d+c = 180
5d = 7c

d+c = 180
5·d = 7·c

c+d = 180
7c-5d = 0

Pivot: Row 1 ↔ Row 2
7c-5d = 0
c+d = 180

Row 2 - 1/7 · Row 1 → Row 2
7c-5d = 0
1.71d = 180


d = 180/1.71428571 = 105
c = 0+5d/7 = 0+5 · 105/7 = 75

c = 75
d = 105

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