Ineed this written as a proportion (equation involving 2 fractions) so i can solve the equation. in a sample of 1500 new iphones, 12 were found defective. at this rate, how many defective iphones would be expected in a sample of 100,000 new iphones?

You can set up a proportion like this:



Notice how the samples are represented in the numerator and the defective iPhones in the denominator.  Since you don't know the number of defective iPhones in the 100,000 sample, you leave it as x.

Use cross multiplication to solve from here:

100000 * 12  =  1500 * x
1200000  =  1500x
x = 800

There are 800 iPhones expected to be defective in a sample of 100,000.