A common denominator, though not the least, is 40.
That's the least common denominator or LCD.
The least common denominator.
That's one fraction. You need at least two to find something in common between them.
There is none. A least common denominator is to be found between or among fractions. 3 and 7 are not fractions.
The least common multiple of two or more denominators is known as the least common denominator, or LCD.
Pick two of the fractions and find the Least Common Multiple of those two denominators. Then take that number, and find the Least Common Multiple between that and the third denominator. This number will be the Least Common Denominator between the three fractions.If you don't care to find the Least common denominator, then just take the three denominators, and multiply them together.