A lot of people jump to a smart number of 100. The confusing part can come when you are asking "what percent of x" (i.e "what percent of 100"). Therefore, you can avoid this by choosing a different smart number which is a multiple of 50 and 25 --> 50.
Therefore:
if X=50
\(\frac{50}{50}\) + \(\frac{50}{25}\) = 1 + 2 = 3
Because we need to figure out the percent of X, we must then take our new fraction \(\frac{3}{50}\) and multiply by 100 to form a percent. Cross multiplication will work fine. \(\frac{3}{50}\) = \(\frac{x}{100}\)
Notice that you can just multiple \(\frac{3}{50}\) * \(\frac{2}{2}\) because this is essentially multiplying by 1 and that will change the denominator to 100 leaving you with \(\frac{6}{100}\) or 6%
Written differently: notice that the denominator in \(\frac{3}{50}\) is 50. Thus, you can make the denominator 100 in order to get a percentage. To do so, you must multiply 50 * 2. Do not forget that if you multiply the denominator by 2, you must also multiply the numerator by 2.
Answer = A