The ratio of boys to girls in a class is 5:7. There are 36 students in the class. How many students are boys?

Boys : Girls : Total    
  5     :  7      : 5 + 7 
  5 .   ;  7 .    : 12

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Find 1 part :
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12 parts = 36 
1 part = 36 ÷ 12
1 part = 3

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Find number of boys (5 parts)
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1 part = 3
5 parts = 3 x 5 
5 parts = 15


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Answer: There are 15 boys.
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