Divisibility by 7 can be checked using a simple method:

1. Take the last digit of the number.
2. Double it, and then subtract this result from the remaining digits of the number.
3. Repeat the process if necessary. If the final result is divisible by 7, then the original number is divisible by 7.

For example, for 203:

• Take the last digit (3), double it (6), subtract from the rest (20): $20 - 6 = 14$.
• Since 14 is divisible by 7, 203 is divisible by 7.

Would you like more details or have any questions?

Here are some related questions:

1. What are other divisibility rules for 2, 3, or 5?
2. Can this rule be applied to larger numbers?
3. Why does this rule work for divisibility by 7?
4. How does divisibility by prime numbers differ from composite numbers?
5. Are there different ways to test divisibility by 7?

Tip: Divisibility rules can help simplify long division and check factors quickly.