DIVISIBILITY OF 7

• Divisibility by 7

– Unfortunately, the rule of thumb for 7 is not

straightforward and you may prefer long division.

– However here is one approach:

• Divisibility of n by 7 is unaltered by taking the last digit

of n

• subtracting its double from the number formed by

removing the last digit from n.

.

Is 3976 divisible by 7?

3976

−12__

385

385

─10__

28

We don’t know if 385

is a multiple of 7 or

not, so we continue

the procedure.

Since 28 is a multiple

of 7, it must be that

both 385 and 3976

are multiples of 7.

x2

x2