If 345,987,091,543,0?4 is divisible by 8, then what can the missing digit be?

1 Answer
Jun 11, 2016

2 or 6

Explanation:

First note that 1000 = 2^3*5^3 is divisible by 8=2^3, so we can ignore the initial 345,987,091,543 part of the number when assessing divisibility by 8.

We can ignore the leading 0 of the remaining 3 digits too.

So we are looking for 2 digit numbers ending in 4 and divisible by 8.

24 = 8 * 3 works

The next solution is 24+40 = 64, since 40 is the least common multiple of 10 and 8.

There are no more solutions since 24 - 40 < 0 and 64 + 40 >= 100