Answer soon it would mean a lot : )

there are 18 boys and 12 girls in a math class .what is the ratio of girls to total students.
a) 18: 30
b) 12: 30
c) 30: 12
d) 30: 18

answer:  

\boxed {\frac{1}{5}}  

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solution-

60 *   \frac{1}{5}   = 12

90 * \frac{1}{5} = 18

75 * \frac{1}{5} = 15

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hence, the answer would be \boxed {\frac{1}{5}}