The last time he checked, matthew was 40 inches tall. matthew just measured himself again and found out that he is 10% taller now. how tall is he now?

44 inches.

All you have to do is find out what 10% of 40 is then add it back to 40. In the case of finding 10% of something you just “chop” of the back number (or move the decimal place forward) so 10% of 40 is 4. The. 40+4=44.

You can also multiply fractions to find the percent of a number but that is not necessary in this case.