Question 1
Editorial self-study SET for 2027; not an official SASMO 2027 examination. Known source years remain in individual attributions. Time: 90 minutes. Platform scoring starts at 0: Q1–15 are worth 2 points each; Q16–25 are worth 4 points each; wrong and blank answers score 0; maximum 70. Official SASMO scoring instead starts at 15, deducts 1 for an incorrect Section A answer and has a maximum of 85. Verified means editorially checked; assumptions, source errors and mathematical uncertainty are disclosed where relevant.
A building has 20 doors numbered 1 to 20. Alex opens all the doors. Bin closes every door whose number is divisible by 2. Cindy closes every door whose number is divisible by 3. Denny closes every door whose number is divisible by 5. Yelly then closes all open doors and opens all closed doors. How many doors are closed at the end?
Enter the numerical answer only.
A building has 20 doors numbered 1 to 20. Alex opens all the doors. Bin closes every door whose number is divisible by 2. Cindy closes every door whose number is divisible by 3. Denny closes every door whose number is divisible by 5. Yelly then closes all open doors and opens all closed doors. How many doors are closed at the end?
Enter the numerical answer only.