What is the Divisibility Test of 21? | How Do You Check Divisibility by 21? | Solved Examples on Divisibility Rule for 21
Are you finding difficulty while calculating the division of the large number by 21 and looking for an easier way to solve it? Then you have stepped into the right guide. Here, we have come up with the divisibility rule for 21. The divisibility rule is a technique that tells whether the given number is divisible by 21 or not in seconds. So, know well about the divisibility rule of 21 like what the 21 divisibility rule is, how to test the number divisible by 21, and worked out examples of the divisibility test for 21. For more information, just dive into this article with no delay:
What is the Divisibility Rule of 21?
There are two simple tricks to check whether the number is divisible by 21 or not. They are as follows:
Rule 1: If the number is divisible by both 3 and 7 then it is divisible by 21.
Rule 2: Multiply the last digit by 2 and subtract with the remaining number. You have to repeat this step till the result gets a single digit and the final number should be divisible by 21. Hence, the given number is divisible by 21.
How To Check If the Number is Divisible by 21 using Divisibility Test of 21?
The step-wise process of finding the number is divisible by 21 with the help of 21 divisibility rules is given below:
Rule 1:
- As per the divisibility rule of 21, see the number is divisible by 3 by adding all the digits.
- See the summation digit is divisible by 3, if it is divisible by 3 then it is divisible by 21.
- Now, apply the divisibility rule of 7 ie., Given number excluding the unit digit - 2 × unit digit.
- If the result is divisible by 7 then it is divisible by 21.
- Remember when the number is divisible by 3 and 7 both then only it is divisible by 21.
Rule 2:
- According to another trick of divisibility by 21, the last digit should be multiplied by 2.
- Now, add the result to the rest of the given number.
- If it is still a large number then repeat the above steps till it is divisible by 21.
- When the result gets divisible by 21 then the original number is divisible by 21.
Solved Examples of 21 Divisibility Rule
Example 1:
Is 4598 divisible by 21?
Solution:
Given the number is 4598
Now, apply the divisibility rule of 21 ie., the number is divisible by both 3 and 7
First, check for divisibility by 3:
Sum of digits = 4+5+9+8 = 26
Verify if it is divisible by 3 ie., 26/3
26 is not divisible by 3
Secondly, check for divisibility by 7:
Double the last digit ie., 8+8 = 16
Subtract the result with the remaining digits in the number ie., 459 -16 = 443
Again double the last digit ie., 3+3 = 6
Subtract 44 - 6 = 38
Check if it is divisible by 7 or not i.e., 38/7
38 is not divisible by 7
Therefore, 4598 is not divisible by 21.
Example 2:
Is 525 divisible by 21?
Solution:
Given the number is 525
Let’s multiply the last digit by 2 ie., 5x2 = 10
Subtract 10 with the remaining number
Ie., 52 - 10 = 42
Check the above result is divisible by 21
Ie., 42 / 21
Yes, 42 is divisible by 21
Hence, 525 is divisible by 21.
What numbers are divisible by 21
List of Numbers divisible by 21: The Numbers 21, 42, 63, 84, 105, 126, 147, 168, 189, 210, 231, 252, 273, 294, 315, 336, 357, 378, 399, 420, 441, 462, 483, 504, 525, 546, 567, 588, 609, 630, 651, 672, 693, 714, 735, 756, 777, 798, 819, 840, 861, 882, 903, 924, 945, 966, 987, 1008, 1029, 1050, 1071, 1092, 1113, 1134, 1155, 1176, 1197, 1218, 1239, 1260, 1281, 1302, 1323, 1344, 1365, 1386, 1407, 1428, 1449, 1470, 1491, 1512, 1533, 1554, 1575, 1596, 1617, 1638, 1659, 1680, 1701, 1722, 1743, 1764, 1785, 1806, 1827, 1848, 1869, 1890, 1911, 1932, 1953, 1974, 1995, 2016, 2037, 2058, 2079, 2100, etc. are divisible by 21.
FAQs on Rule of Divisibility by 21
How To Tell if the number is divisible by 21?
If the number is exactly divisible by 21 then it should be divisible by 3 and 7 both.
How do you determine the number is divisible by 21?
To determine whether a number is divisible by 21, the last digit must be multiplied by 2 and the result needs to be subtracted from the remaining digits in the given number. When the end result is divisible by 21 then the given number is divisible by 21.
Is 2373 divisible by 21 yes or no?
Yes, 2373 is divisible by 21.
Summary
We hope the knowledge shared on the divisibility rule for 21 helped you a lot while doing homework or assignments. Want to check all other divisibility rules from 1 to 25? Simply visit the roundingcalculator.guru and test whether the number is divisible or not.
