Created By : Jatin Gogia
Reviewed By : Rajasekhar Valipishetty
Last Updated : Apr 06, 2023
Free LCM Calculator determines the least common multiple (LCM) between 4 and 21 the smallest integer that is 84 that is divisible by both numbers.
Least Common Multiple (LCM) of 4 and 21 is 84.
LCM(4,21) = 84
Least common multiple or lowest common denominator (LCD) can be calculated in three ways;
Least common multiple can be found by multiplying the highest exponent prime factors of 4 and 21. First we will calculate the prime factors of 4 and 21.
Prime Factorization of 4
2 | 4 |
2 | 2 |
1 |
Prime factors of 4 are 2. Prime factorization of 4 in exponential form is:
4 = 22
Prime Factorization of 21
3 | 21 |
7 | 7 |
1 |
Prime factors of 21 are 3,7. Prime factorization of 21 in exponential form is:
21 = 31×71
Now multiplying the highest exponent prime factors to calculate the LCM of 4 and 21.
LCM(4,21) = 22×31×71
LCM(4,21) = 84
Factors of 4
List of positive integer factors of 4 that divides 4 without a remainder.
1, 2, 4
Factors of 21
List of positive integer factors of 21 that divides 21 without a remainder.
1, 3, 7, 21
The formula of LCM is LCM(a,b) = ( a × b) / GCF(a,b).
We need to calculate greatest common factor 4 and 21, than apply into the LCM equation.
GCF(4,21) = 1
LCM(4,21) = ( 4 × 21) / 1
LCM(4,21) = 84 / 1
LCM(4,21) = 84
(i) The LCM of 21 and 4 is associative
LCM of 4 and 21 = LCM of 21 and 4
1. What is the LCM of 4 and 21?
Answer: LCM of 4 and 21 is 84.
2. What are the Factors of 4?
Answer: Factors of 4 are 1, 2, 4. There are 3 integers that are factors of 4. The greatest factor of 4 is 4.
3. What are the Factors of 21?
Answer: Factors of 21 are 1, 3, 7, 21. There are 4 integers that are factors of 21. The greatest factor of 21 is 21.
4. How to Find the LCM of 4 and 21?
Answer:
Least Common Multiple of 4 and 21 = 84
Step 1: Find the prime factorization of 4
4 = 2 x 2
Step 2: Find the prime factorization of 21
21 = 3 x 7
Step 3: Multiply each factor the greater number of times it occurs in steps i) or ii) above to find the lcm:
LCM = 84 = 2 x 2 x 3 x 7
Step 4: Therefore, the least common multiple of 4 and 21 is 84.