Find the LCD 7/8 , 9/10

Find the values of the numerical part of each term. Select the largest one, which in this case is ${\displaystyle 10}$. Multiply them together to get the current total. In this case, the current total is ${\displaystyle 80}$.

Current Total = ${\displaystyle 80}$

Multiply the numeric part of the denominators together.

Current Total = ${\displaystyle 10+10=20}$

Multiply the numeric part of the denominators together.

Current Total = ${\displaystyle 20+10=30}$

Multiply the numeric part of the denominators together.

Current Total = ${\displaystyle 30+10=40}$

Check each value in the numerical part of each term against the current total. Since the current total is evenly divisible, return it. That is the least common denominator of the numerical part of the fraction.