Quick tests for ÷2, 3, 4, 5, 6, 9 and 10 — no long division needed
Change the number with − and +, pick a divisor, and see which rule applies.
Number
Divisor
Rule for 3
A number is divisible by 3 when the sum of its digits is divisible by 3.
Digit sum is 12 — 12 ÷ 3 ✓.
246 ÷ 3: Yes — divisible!