Final answer:
The least common denominator for fractions 9/10 and 7/8 is 40, found by identifying the least common multiple of the denominators 10 and 8.
Step-by-step explanation:
The least common denominator (LCD) for the fractions 9/10 and 7/8 can be found by identifying the smallest number that both denominators (10 and 8) can divide into. To find the LCD by intuition, we can analyze the prime factors of 10 (2 and 5) and 8 (23) and then find the least common multiple (LCM) of these factors, which is 23 * 5 = 40. Therefore, the least common denominator for 9/10 and 7/8 is 40.