Olympiad workbook
- Exam
- Olympiad workbook
- Subject
- IOQM
- Chapter
- Basics of Mathematics
Olympiad workbook · IOQM · Basics of Mathematics
For a natural number n , let n^ denote the number obtained by...
For a natural number , let denote the number obtained by deleting zero digits, if any. (For example, if ; if , .) Find the number of 3 -digit numbers n for which is a divisor of , different from .
Correct answer
93
Step-by-step solution
\because n^{\prime} \neq nn=\overline{a b c}c=0 \Rightarrow \overline{a b} \mid \overline{a b c}
\Rightarrow \overline{a b} \mid 10 \overline{a b}n=9 \times 9=81b=0 \Rightarrow \overline{a c} \mid \overline{a b c}
10 a=8 c8 c-10 a=\lambda(10 a+c)\lambda10 a=8 c \Rightarrow 5 a=4 c \Rightarrow(a, c)=(4,5)c(8-\lambda)=10 a(\lambda+1) \Rightarrow c=a
for \left(\frac{20}{7}\right)\lambda=2, c=5 a \Rightarrow(a, c)=(1,5)\lambda=3, c=8 a \Rightarrow(a, c)=(1,8)\lambda=4, c=a (Not possible)
and no further value of is needed to be checked
Number of numbers , which are 405,105 and 108.
Case III. If both , then all values of are acceptable.
Number of numbers
So total number of possible values of .