The House On Your street are numbered with odd numbers starting with 1 and ending with 201. How many house numbers contain at least one 7?

Question

aaronq · Answer

you have 200 numbers, there is a seven in every ten numbers 1-10. so $\sf 20$

There is also the 70's series: 70, 71, 72, 73.. 79. so the 10 more numbers, but since we already counted 77 in the previous part, we subtract 1, so $\sf 9$.

This happens again in 170's series.

SO in total you have:  $\sf 20 + 9 + 9$

goformit100 · Answer

Sir/Ma'am, A Warm Welcome To Open Study.