Pop the Number
Pop every multiple of 7. Leave the impostors floating.
Multiples of 7 have no neat digit trick, unlike 2, 5 or 10, so this one is pure recall plus a check. Run up the table in steps of 7 and see whether your number appears: 7, 14, 21, 28, 35, 42, 49, 56, 63, 70. If it does not appear, it is not a multiple, however close it looks. The traps here were 27 (just under 28), 40 (between 35 and 42), 44 (between 42 and 49) and 54 (between 49 and 56). When you are unsure, find the nearest multiple you do know and count on in sevens from there.
What to say if they get stuck
- Say the seven times table under your breath: 7, 14, 21, 28, 35, 42, 49, 56, 63, 70.
- A number is a multiple of 7 only if 7 divides into it with nothing left over.
- Watch out for the near misses. 27, 40, 44 and 54 all sit between two multiples of 7 without being one.