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Mathematics

Grade5

Easy

Question

Find the lowest common denominator of the fractions $2 over 7$ and $2 over 21$ .

7
21
18
147

hint Hint:

In this question we have to find the least common denominator and for that we have to find the least common multiple of denominators. Least Common Denominator (LCD) is the least common multiple of denominator of a set of fractions. The method of calculating the LCD is same as calculation of Least Common Multiple of fractions denominators. The least common multiple (LCM) of two numbers is the lowest possible number that can be divisible by both numbers.

The correct answer is: 21

The least common denominator is the lowest common multiple of the denominators of a set of fractions.
Step1: We are given fractions $2 over 7$ and $2 over 21$ .
And we have to find the LCM of denominators of the fractions i.e., $7$ and $21$ .
Step2: We know that Multiples of   $7$ are: $7 comma 14 comma 21 comma 28 horizontal ellipsis$
And the multiples of $21$ are: $21 comma 42 comma 63 horizontal ellipsis$
Step3: Now we have to find the LCM of   $7$ and $21$
From the above multiples of   $7$ and $21$ it can be easily seen that the least common multiple of is $21$ .
Hence the least common denominator of $2 over 7$ and $2 over 21$ is 21.
Multiples of 7 are 7, 14, 21, 28…
Multiples of 21 are 21, 42, 63…
The least common denominator of $2 over 7$ and $2 over 21$ is 21.

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