if it's 25% off, then the new price is 75% of the old price
so multiply 75% or 0.75 by 24 = 18
or you could do it this way:
25% is 1/4. so to get 1/4 of 24 divide: 24/4 = 6 (the discounted amount)
then subtract: 24 - 6 = 18
so either percentages or fractions!