Answer:
To distribute books equally among students of section A or B, we need to have a common factor that divides both 30 and 28. The common factor of 30 and 28 is 2.
So, we need to find the least common multiple (LCM) of 30 and 28, which is the smallest multiple that 30 and 28 have in common.
The prime factorization of 30 is 2 x 3 x 5, and the prime factorization of 28 is 2 x 2 x 7.
To find the LCM, we take the highest power of each prime factor that occurs in either number:
LCM = 2 x 2 x 3 x 5 x 7 = 420
Therefore, we need at least 420 books for the class library, so that they can be distributed equally among students of section A or B.