What is the least common denominator of 2, 8, 5, and 7?
2 = 2
8 = 2 * 2 * 2
5 = 5
7 = 7
It's like we're making a parts list. In this case our parts list is 2 * 2 * 2 * 5 * 7 because that's the list that has enough parts to make 2, 8, 5, or 7.
2 * 2 * 2 * 5 * 7 = 280
Answer: The LCD is 280.
.
Which of 5 1/2, 5 5/8, 5 2/5, 5/7 is bigger?
5 1/2 = 11/2
5 5/8 = 45/8
5 2/5 = 27/5
5/7 = 5/7
We want to convert all of these to something / 280 (the LCD).
5 1/2 = 11 / 2 * 140 / 140 = 1540 / 280
5 5/8 = 45 / 8 * 35 / 35 = 1575 / 280
5 2/5 = 27 / 5 * 56 / 56 = 1512 / 280
5/7 = 5 / 7 * 40 / 40 = 200 / 280
Since 1575 / 280 is the biggest of those fractions, 5 5/8 is the biggest of the original numbers.