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 #1
avatar+834 
+1

We can analyze this problem by considering the divisibility rules for 2, 3, 4, 5, 6, 8, and 9:

 

Divisibility Rules:

 

A number is divisible by 2 if the last digit is even (0, 2, 4, 6, or 8).

 

A number is divisible by 3 if the sum of its digits is divisible by 3. (Given in the problem statement)

 

A number is divisible by 4 if the last two digits are divisible by 4. (Not applicable here since the number ends in 0)

 

A number is divisible by 5 if the last digit is a 0 or a 5.

 

A number is divisible by 6 if it's divisible by both 2 and 3.

 

A number is divisible by 8 if the last three digits are divisible by 8. (Not applicable here since the number ends in 0)

 

A number is divisible by 9 if the sum of its digits is divisible by 9. (This is similar to the divisibility rule for 3, but a stronger condition)

 

Analysis:

 

Ending in 0: Since the number ends in 0, it is automatically divisible by 2 and 5 (based on the divisibility rules).

 

Sum of Digits Divisible by 3: The problem states that the sum of the digits is divisible by 3. This means the number itself must also be divisible by 3 (based on the divisibility rule for 3).

 

Divisibility by Other Numbers:

 

Looking at the remaining numbers (4, 6, 8, and 9), we can see that:

 

4: Not necessarily divisible. Just because the last digit is 0 (divisible by 2), it doesn't guarantee divisibility by 4 (requires the last two digits to be divisible by 4).

 

6: Since the number is divisible by both 2 (ending in 0) and 3 (given in the problem statement), it is automatically divisible by 6.

 

8: Not necessarily divisible. Similar to 4, just because the number ends in 0 (divisible by 2), it doesn't guarantee divisibility by 8 (requires the last three digits to be divisible by 8).

 

9: Not necessarily divisible. The sum of digits being divisible by 3 is a weaker condition than being divisible by 9. So, a number divisible by 3 might not necessarily be divisible by 9.

 

Conclusion:

 

Therefore, a number ending in 0 with a sum of digits divisible by 3 is necessarily divisible by 2, 3, and 6 (out of the given numbers). There are 3​ such divisors.

May 25, 2024
 #1
avatar+964 
0

I can answer problem 2!

 

This problem can be solved by analyzing the behavior of the function f(x, y) at different points and identifying repeating patterns.

 

Understanding the Function:

 

The function f(x, y) modifies the x and y coordinates based on the initial values of x and y.

 

If x > 4, it subtracts 4 from x and keeps y the same. (e.g., f(5, 1) = (1, 1))

 

If x <= 4 and y > 4, it keeps x the same and subtracts 4 from y. (e.g., f(2, 5) = (2, 1))

 

Otherwise (x <= 4 and y <= 4), it adds 5 to x and adds 2 to y. (e.g., f(1, 1) = (6, 3))

 

Analyzing the Robot's Movement:

 

Starting Point: The robot starts at (1, 1).

 

First Iteration: Applying f(1, 1) based on the third rule (x <= 4 and y <= 4), we get f(1, 1) = (6, 3).

 

Subsequent Iterations:

 

At (6, 3), x > 4 and y > 4. So, f(6, 3) = (2, -1). (This is because x is now greater than 4, and y is greater than 4 in the new position).

 

At (2, -1), x <= 4 and y <= 4. So, f(2, -1) = (7, 1).

 

At (7, 1), x > 4 and y <= 4. So, f(7, 1) = (3, 1).

 

Repeating Pattern:

 

Notice how the robot's movement falls into a repeating cycle: (1, 1) -> (6, 3) -> (2, -1) -> (7, 1) -> (3, 1) -> (8, 3) -> ...

 

This cycle repeats because after reaching (3, 1), the function follows the same path back to (1, 1) and continues the cycle infinitely.

 

Number of Unique Points:

 

Within this cycle, there are 4 unique points visited: (1, 1), (6, 3), (2, -1), and (7, 1).

 

Therefore, the robot will visit only 4 unique points regardless of how long it runs.

May 25, 2024
May 24, 2024
 #1
avatar+1894 
0

https://web2.0calc.com/questions/coordinates_9298

 

Very well done here!

 

Thanks! :)

May 24, 2024

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