The ratio of the number of boys and girls in a school is 3: If 20% of the boys and 25% of the girls are scholarship holders, what percent of the students are not scholarship holders?

 To change a ratio to two fractions, put each number, 3 and 2, over the sum of the two numbers 3+2, or 5. So the two fractions are {{{3/5}}} and {{{2/5}}}. That means {{{3/5}}}ths of the students are boys and {{{2/5}}}ths of the students are girls. Change those to percents: {{{3/5=60/100="60%"}}}, {{{2/5=40/100="40%"}}} So 60% of the students are boys and 40% of the students are girls. 

 That means 20% of 60% are boy scholarship holders and 25% of 40% are girl scholarship holders. Therefore: 20% of 60% = (0.20)(0.60) = 0.12 = 12% of the students are boy scholarship holders, and 25% of 40% = (0.25)(0.40) = 0.10 = 10% of the students are girl scholarship holders. That me