84
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3: 3 28: 7, 2, 2 21: 7, 3 LCM = 3x7x4 = 84
LCM of 7 and 28 is 28.
LCM(21, 28, 42) = 84
To find the Least Common Multiple (LCM) of 7, 14, and 21, we first need to factorize each number. The prime factors of 7 are 7, of 14 are 2 x 7, and of 21 are 3 x 7. To find the LCM, we take the highest power of each prime factor that appears in any of the numbers. Therefore, LCM(7, 14, 21) = 2 x 3 x 7 = 42.
First you express the numbers as the product of their prime factors: 28 = 2x2x7 21 = 3x7 Next you find the HCF. In this case, the HCF is 7. Finally, you multiply the numbers together and divide by the HCF. 28x21/7 = 84 Therefore the LCM of 28 and 21 is 84.