The expression "1000/400" represents a division problem where 1000 is divided by 400. This calculation results in 2.5, meaning that 1000 is two and a half times larger than 400. Division is a fundamental arithmetic operation used to determine how many times one number fits into another. In practical terms, this division can be applied in various contexts, such as calculating ratios or proportions. For example, if you have 1000 units of a product and want to distribute them into groups of 400, you can create 2 full groups with 200 units remaining.