- #1
Robert Houdart
- 11
- 0
Homework Statement
An intelligence agency forms a code of two distinct digits selected from 0, 1 , 2…, 9, such that the first digit of the code is nonzero. The code, handwritten on a slip, can, however, potentially create confusion when read upside down - for example; the code 91 may appear as 16. How many codes are there for which no such confusion can arise?
2. The attempt at a solution
This is the methodology I used:
Since the first digit cannot be zero, therefore it can be chosen in 9 ways while no restriction occurs on the second number, therefore it can be chosen in 10 ways.Thus, the total number of ways is 10*9=90...
Since 1,6,8,9 can create confusion, therefore there exist 12 such numbers which will create confusion. However the pair 69 and 96 do not come under this category.