posted by Student56 .
There are 175 pupils in a hall. 40% of them are boys. 25 girls enter the hall. What percentage of the pupils in the hall now are boys?
Start off by figuring out 40% (percent means you take 40 and divide it by 100) of ("of" means multiply) 175.
(40/100) x 75 = ?
That will tell you how many boys there are now.
Next, figure out how many girls there are now. (How many are left over?)
Add 25 to the girls' number (since 25 girls just walked in). Add 25 to 175 people (since 25 people just walked in).
"New number of girls" divided by "new number of people" gives you the percentage. (It will be higher than 60%, just as a control of error).