You simple subtract 75-25=50 after that you use the base which is 75 people so it will be= 50/75 if you put this as a decimal 50/75=0.6666666(it goes on) you have to remember you need to multiply it by x100 with that you get 66.6 if you need to round it will be 66.7 (by tenth) by whole 7.
