Oh, this is very easy! Here, I'll explain it to you. This type of problem is trying to find a proportion. A proportion is two ratios that are equivalent to one other, where the means are equivalent to the means, and the extremes are equivalent to the extremes. What are those you may ask? Well, here are two sets of ratios: 3:15 and 18:6 Remember that ratios could be written as a fraction form, so they would also look like this: 3/15 and 18/6 So, now, there are the means, which would be 15 and 18, because they are on opposite positions, (15 is the denominator, and 18 is the numerator, and the denominator and numerator are opposite positions). The best way I remember it is to first write the ratio from a fraction version to the semi colon version. (3:15 and 18:6). You see how 15 and 18 are close to each other? Those numbers are called the means. Now 3 and 6 are on the opposite sides, which are called the extremes. You could also remember extremes as "extremely far from each other". So, in order to see if they are equal to one-another, you must multiply the means by the means, (15 times 18), which would be 270, and now we have to multiply the extremes by the extremes, (3 times 6), which would be 18. Now we have to see if our answers from the means and extremes are the same. 270 and 18 are NOT the same numbers, (the same numbers would be 270 and 270, or 18 and 18), so we could say that they are NOT proportional. Now, to solve 7/n and x/3. we have to first put it in semi colon form, which would be 7:n and x:3. The next step is to multiply the extremes first, because they are the actual numbers we have. 7 times 3 equals 21, so now we must make the means' answer the same. We could do 7:21 and 1:3, because 21 times 1 equals 21, which is the same answer as 21, (21 is the extremes' answer). Now they are proportional, (proportional also means equal), and we have solved this problem. Well done following along the way, and I hope I helped! :-)
