SPM 2019 Add Maths Paper 1, Question 22Permutation & Combination

Solved on video in English and Bahasa Melayu · 3 marks · Form 5, Permutation & Combination · 4:56 video

The question

Diagram 9 shows a four-digit passcode '0131' set by San on his smartphone. He wants to reset the passcode such that the new passcode cannot consist of digit 1 followed by digit 3. How many different passcodes can be formed?

[3 marks]

SPM 2019 Add Maths Paper 1, Question 22: the question as drawn in Eduly's video4:56

Step 1

Total possible 4-digit passcodes (each of the 4 digits can independently be 0-9): 10 x 10 x 10 x 10 = 10 000.

Why this step

A passcode can repeat digits and can start with 0, so all 4 positions have the full 10 choices and we multiply.

6 more steps, each with the reason for it, in the full solution

Final answer

9701

Where students lose marks

Watch out: 1313 is counted twice when you add the three patterns. Subtract 1 once, or you get 9700 instead of 9701.

Watch every step of this question solved on video (4:56), with the reason behind each step and a box that checks your own answer.

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