Answer
3600
Work Step by Step
The Least Common Multiple is the smallest number that is a multiple of all of the numbers listed. Remember, multiples of a number are all of the numbers that the number can be multiplied by a whole number to get that number. Thus, we find the multiples of each number until we get a common multiple:
$$ 400: 400,800,1200,1600,2000,2400,2800,3200,3600 \\ 1800: 1800, 3600$$
The LCM is 3600.
