If we let x equal the first number, then the next number has to be x + 5 (since they are multiples of 5) and the next would be x + 10. Now we just add them and set them equal to 75...
x + x+5 + x+10 = 75
Combine like terms
3x + 15 = 75
subtract 15 from each side
3x = 60
divide each side by 3
x = 20
So the least number is 20
*Now let's check to make sure we are right...
20 + 25 + 30 = 75
75 = 75 True... It checks!
