Question

Write down all the two-digit numbers that can be made using the digits 1,5 and 7.

Each digit can be repeated.
(3 marks)

Answer 1

11,15,17,55,57,77,51,71,75,51

Explanation:

Answer 2

1,2,5,7,8 and 9. Thus, we have 6 numbers. Then we want to form two-digit numbers without repetition. There are 6 number that is possible to occupy first digit, right? 1,2,5,7,8 or 9. Because it’s without repetition, so the number that have been filled the first digit cannot be the second digit. Thus, the numbers that is possible to occupy second are 5 digits. Thus, there are 6 x 5 = 30 numbers that can we form from those 6 numbers: 1,2,5,7,8 and 9 without repetition.

or by using permutation, there are two place would be filled by six number, so the permutation is 6P2 = 6!/ (6–2)! = 6!/4! = 6 x 5 = 30.

Explanation: