Answer: 252
Step-by-step explanation:
LCM is Least Common Multiple
You can do this the long way (by find the multiples of each and seeing which one they have in common):
Multiples of 42: 42, 84, 126, 168, 210, 252
Multiples of 63: 63, 126, 189, 252
Multiples of 84: 84, 168, 252
The first multiple they have in common is 252
or
You can do this by finding their prime factorization, identifying what they have in common, and multiplying the "left overs".
Prime factorization of 42: 2 · 3 · 7
Prime factorization of 63: 3 · 3 · 7
Prime factorization of 84: 2 · 2 · 3 · 7
Common factors (common to at least two of the terms) are: 2 · 3 · 7 = 42
Left overs (see bolded numbers above) are: 2 · 3 = 6
Common terms x left overs = LCM: 42 x 6 = 252
