Divisibility Rule of 81

The divisibility rule for 81 is a method by which we can find out if a number is divisible by 81 or not without using the division method. Check whether 729 is divisible by 81 with the divisibility rule.

Step 1: Check if the sum of the digits of the number is divisible by 9. For 729, the sum is 7 + 2 + 9 = 18. Since 18 is divisible by 9, proceed to the next step.

Step 2: Divide the number by 9. If the result is still divisible by 9, then the original number is divisible by 81. For 729, 729 ÷ 9 = 81. Since 81 is divisible by 9, 729 is divisible by 81.

Learning the divisibility rule will help kids to master division. Let’s learn a few tips and tricks for the divisibility rule of 81.

Know the multiples of 81:

Memorize the multiples of 81 (81, 162, 243, 324, etc.) to quickly check divisibility.

Use the sum of digits:

If the sum of the digits is not divisible by 9, then the number is not divisible by 81.

Repeat the process for large numbers:

For very large numbers, break them down into parts that can be easily summed up. For example, check if 7290 is divisible by 81 using the divisibility test. The sum of digits is 7 + 2 + 9 + 0 = 18, which is divisible by 9, hence divide 7290 by 9, resulting in 810. Since 810 is divisible by 9, 7290 is divisible by 81.
 

Use the division method to verify:

Students can use the division method as a way to verify and cross-check their results. This will help them to verify and also learn.

• Divisibility rule: A set of guidelines used to determine if a number can be divided by another number without a remainder.

• Multiples: Numbers obtained by multiplying a given number by an integer. For example, multiples of 81 are 81, 162, 243, etc.

• Integers: Whole numbers that include positive numbers, negative numbers, and zero.

• Sum of digits: The total obtained by adding all the digits of a number.

• Verification: The process of confirming whether a calculation or result is accurate, often by using a different method.