I forgot the last digit of a 7-digit telephone number. If I randomly dial the final 3 digits after dialing the first four, then what is the chance of dialing the correct number?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → \(\frac{1}{1000}\)
Each of the three digits dialled at random can be any of the ten digits 0 to 9, and only one of all the possible endings is the right number.
Possible endings: \(10\times10\times10=1000\), all equally likely
Favourable endings: 1 (the correct last three digits)
Probability: \(\frac{1}{1000}\)