# Thread: 3digit numbers that are multiples of 7 with individual digits that add to 7.

1. ## 3digit numbers that are multiples of 7 with individual digits that add to 7.

how can i find all the 3 digit numbers that are multiples of seven with individual digits that add to 7? I've been trying to figure this out using modular arithmetic, but I think I'm doing it wrong.

2. Originally Posted by qtpipi
how can i find all the 3 digit numbers that are multiples of seven with individual digits that add to 7?
Using the floor function $\left\lfloor {\dfrac{{999}}{7}} \right\rfloor - \left\lfloor {\dfrac{{99}}{7}} \right\rfloor$.

Tell us why that works.

3. the floor function just gives us the number of 3 digit numbers that are multiples of 7. i need to find which of these multiples of 7 have individual digits that add to 7.

4. Originally Posted by qtpipi
the floor function just gives us the number of 3 digit numbers that are multiples of 7. i need to find which of these multiples of 7 have individual digits that add to 7.
Sorry, I read the question too quickly.

5. figured it out!