Rule 7 in math refers to the divisibility rule of 7, which helps determine if a number is divisible by 7 without actually performing the division.
Here's how the rule works:
- Double the last digit of the number.
- Subtract this doubled value from the remaining digits of the original number (excluding the last digit).
- If the result is divisible by 7, then the original number is also divisible by 7.
Example:
Let's check if the number 357 is divisible by 7.
- Double the last digit (7): 7 x 2 = 14
- Subtract 14 from the remaining digits (35): 35 - 14 = 21
- Since 21 is divisible by 7, the original number 357 is also divisible by 7.
Important Note: If the result obtained after subtracting is not divisible by 7, you can repeat this process until you get a result that is clearly divisible or not divisible by 7.
Variations of the Rule:
Some variations of the rule exist, like adding five times the last digit to the remaining digits. However, the core concept remains the same: perform a simple calculation to simplify the divisibility check.
This rule is a useful tool for:
- Quickly checking divisibility of large numbers.
- Simplifying calculations when dealing with multiples of 7.
