Academy 23151

There are 180 pupils in the first year of the academy. Seven girls for every five boys, so there are how many girls 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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