Math CentralQuandaries & Queries


Question from celeste, a student:

18/y=30/25 what number does y represent

Hi Celeste,

This is a question about equivalent fractions. You want a fraction that is equivalent to $\frac{30}{25}$ which has a numerator of 18.

Start with the fraction $\frac{30}{25}.$ Is there an integer, larger than 1 that divides 30 and 25? Divide 30 and 25 by this integer to form a second fraction that is equivalent to $\frac{30}{25}.$ Look at this second fraction. By what number do you need to multiply its numerator to obtain 18? Multiply the numerator and denominator of the second fraction by this number to obtain a frraction, equivalent to the second fraction and hence equivalent to $\frac{30}{25}$ that has a numerator of 18.


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