Final answer:
To find the least common denominator of the four fractions, convert each mixed number to an improper fraction and find the least common multiple (LCM) of the denominators. The least common denominator of the four fractions is 100.
Step-by-step explanation:
To find the least common denominator of the four fractions, we can start by converting each mixed number to an improper fraction.
20 7/10 = 20 + 7/10 = 207/10
20 3/4 = 20 + 3/4 = 203/4
18 9/10 = 18 + 9/10 = 189/10
20 18/25 = 20 + 18/25 = 1420/25
Now, we can find the least common multiple (LCM) of the denominators: 10, 4, 10, and 25.
The LCM of 10, 4, 10, and 25 is 100. Therefore, the least common denominator of the four fractions is 100.