210
LCD(9, 21) = 63
LCD(18, 21) = 126
You can't accurately compare fractions if they don't have a common denominator. In other words, the bottom numbers of both fractions have to be the same. To change that, you have to find the LCD, or least common denominator (the smallest number both bottom numbers multiply evenly into.) In this case, the LCD is 30, since 3 is a factor of 30. Since 10 x 3 =30, we have to multiply the top number (or numerator) by 10 also. Here's what the process looks like: 21/30 > 2/3 (original problem) 21/30 > ?/30 (find the LCD) 21/30 > 20/30 (multiply the numerator by the same number as the denominator) 21/30 > 20/30 (final answer) So there you have it. 21 is larger than 20, therefore 21/30 is larger than 2/3.
LCD(21, 13, 14, 15) = 2730
30
21
It is 30
LCD(49, 21) = 147
21
It is: 105
21.
No.