Find the least common multiple of 8, 15, and 21. . . . . . It's 280 .
So all the numbers divisible by 8, 15, and 21 are all the multiples of 280.
The smallest 6-digit number is 100,000 .
100,000 / 280 = 357.1 , so the next whole-number multiple is the 358th one.
280 x 358 = 100,240 .
You can tell right away that this is the smallest one that qualifies,
because if you take away 280 and go to the next smaller multiple,
it won't have 6 digits anymore.
