The terms you've provided, "1-3" and "2-7," appear to be fractions written as "1/3" and "2/7." To find the least common denominator (LCD) of these two fractions, we follow these steps:

1. Identify the denominators: The denominators are 3 and 7.
2. Find the least common multiple (LCM) of these denominators.

The LCM of 3 and 7 is 21 because 3 and 7 are both prime numbers, and their product (3 × 7 = 21) is the smallest number that both 3 and 7 divide evenly into.

Thus, the least common denominator (LCD) of 1/3 and 2/7 is 21.

Would you like more details or have any questions about this process?

Here are 5 related questions:

1. How do you convert fractions to have the same denominator?
2. How do you add or subtract fractions with different denominators?
3. What is the greatest common divisor (GCD) and how is it different from the LCM?
4. How do you simplify fractions after finding a common denominator?
5. How can you determine the LCD of three or more fractions?

Tip: When finding the least common denominator, it's useful to break the denominators into their prime factors, making it easier to identify the LCM.