Deceptively Simple Integer Problem

  • Thread starter chillfactor
  • Start date
  • Tags
    Integer
In summary, the total number of 7's in the given range is 38, not 40. This is because there are 20 7's in the every tenth number group, 8 in the 70's group, and 8 in the 170's group. However, two numbers (77 and 177) are counted twice, giving a total of 38 7's.
  • #1
chillfactor
12
0
[b

Homework Equations



none

The Attempt at a Solution

Homework Statement


Homework Equations


The Attempt at a Solution

 
Last edited:
Physics news on Phys.org
  • #2
You're forgetting to add 71, 72, 73, ...,76, 78, 79 and 171, 172, 173, ...,176, 178, 179
 
  • #3
Well you know that for the hundreds it does not appear once, since the problem does not go up to 700. As for the tens you get all the all the 70's (70 through 79) and all the 170's (170 through 179). As for the ones you get one every 10 digits (7, 17, 27...187, 197).


I do not get why the answer is 38 instead of 40. Like you said, there are 1 7 every 10 numbers, which gives you 20 7's, But if you add 70...79 and 170...179 together, you get 20 more 7's, which gives you a grand total of 40 7's.
 
  • #4
morrowcosom said:
Well you know that for the hundreds it does not appear once, since the problem does not go up to 700. As for the tens you get all the all the 70's (70 through 79) and all the 170's (170 through 179). As for the ones you get one every 10 digits (7, 17, 27...187, 197).


I do not get why the answer is 38 instead of 40. Like you said, there are 1 7 every 10 numbers, which gives you 20 7's, But if you add 70...79 and 170...179 together, you get 20 more 7's, which gives you a grand total of 40 7's.
You counted two numbers twice: 77 and 177.

Every tenth number starting with 7: {7, 17, 27, 37, ..., 77, 87, ...,167, 177, 187, 197}
70's group: {70, 71, 72, ... , 76, 77, 78, 79}
170's group: {170, 171, 172, ... , 176, 177, 178, 179}
 

Related to Deceptively Simple Integer Problem

What is the "Deceptively Simple Integer Problem"?

The "Deceptively Simple Integer Problem" is a mathematical problem that involves finding the sum of two integers that are seemingly easy to solve, but actually require more complex techniques to accurately determine the solution.

What makes the "Deceptively Simple Integer Problem" challenging?

The "Deceptively Simple Integer Problem" is challenging because it requires critical thinking and problem-solving skills to identify the underlying complexities and determine the correct solution. It also tests one's ability to think outside the box and not be deceived by the seemingly straightforward nature of the problem.

What are some common mistakes people make when attempting to solve the "Deceptively Simple Integer Problem"?

Some common mistakes people make when solving the "Deceptively Simple Integer Problem" include assuming that the solution is a single digit number or not considering the order of operations. They may also overlook the possibility of negative numbers or not fully understanding the problem, leading to incorrect calculations.

Are there any strategies for solving the "Deceptively Simple Integer Problem"?

Yes, there are strategies for solving the "Deceptively Simple Integer Problem." These include carefully reading and understanding the problem, breaking it down into smaller parts, and considering all possible scenarios. Additionally, keeping track of calculations and double-checking answers can help avoid mistakes.

What real-world applications does the "Deceptively Simple Integer Problem" have?

The "Deceptively Simple Integer Problem" has various real-world applications in fields such as computer science, cryptography, and finance. It can also help improve critical thinking skills and problem-solving abilities, which are valuable in any profession.

Similar threads

  • Precalculus Mathematics Homework Help
Replies
5
Views
889
  • Precalculus Mathematics Homework Help
Replies
6
Views
1K
  • Precalculus Mathematics Homework Help
Replies
18
Views
345
  • Precalculus Mathematics Homework Help
Replies
4
Views
2K
  • Precalculus Mathematics Homework Help
Replies
4
Views
1K
  • Precalculus Mathematics Homework Help
Replies
6
Views
758
  • Precalculus Mathematics Homework Help
Replies
15
Views
2K
  • Precalculus Mathematics Homework Help
Replies
4
Views
4K
  • Precalculus Mathematics Homework Help
Replies
19
Views
1K
  • Precalculus Mathematics Homework Help
2
Replies
35
Views
5K
Back
Top