Divisibility Rule of 79

The divisibility rule for 79 is a method to find out if a number is divisible by 79 without using division. Check whether 6321 is divisible by 79 using the divisibility rule.  

Step 1: Multiply the last digit of the number by 23, here in 6321, 1 is the last digit. Multiply it by 23. 1 × 23 = 23.  

Step 2: Subtract the result from Step 1 from the remaining number without the last digit. i.e., 632–23 = 609.  

Step 3: Check if 609 is a multiple of 79. Since it is not, 6321 is not divisible by 79. If the result from step 2 is a multiple of 79, then the number is divisible by 79.

Learning the divisibility rule helps kids master division. Let’s learn a few tips and tricks for the divisibility rule of 79.

Know the multiples of 79:

Memorize the multiples of 79 (79, 158, 237, etc.) to quickly check divisibility. If the result from the subtraction is a multiple of 79, then the number is divisible by 79.

Use negative numbers:

If the result after subtraction is negative, ignore the negative sign and consider it as positive for checking divisibility.

Repeat the process for large numbers:

Students should keep repeating the divisibility process until they reach a small number that can be checked for divisibility by 79.  

For example: Check if 15842 is divisible by 79 using the divisibility test.  Multiply the last digit by 23, i.e., 2 × 23 = 46.  

Subtract 46 from the remaining digits, excluding the last digit: 1584–46 = 1538.  

Repeat the process: 8 × 23 = 184.  Subtract 184 from the remaining digits, excluding the last digit: 153–184 = -31.  

Since -31 is not a multiple of 79, 15842 is not divisible by 79.

Use the division method to verify:

Students can use the division method to verify and cross-check their results. This will help them confirm their understanding.

• Divisibility rule: A set of rules used to determine whether a number is divisible by another number without performing division.

• Multiples: The results obtained by multiplying a number by an integer. For example, multiples of 79 are 79, 158, 237, etc.

• Integers: Numbers that include all whole numbers, negative numbers, and zero.

• Subtraction: The process of finding the difference between two numbers by reducing one from another.

• Verification: The process of confirming the correctness of a result, often by using an alternative method such as division.