Question

Eric's notebook has 30 pages. he wants to writes a number on each page. how many digits will he write when he numbers all the pages in the notebook?
a. 9
b. 29
c. 49
d. 51

Answer 1

the answer is d (i.e. 51).
the first 9 pages utilize 9 digits. the remaining 21 pages utilize two digits number. Therefore,
21*2=42
the total is 42+9=51