Either I need my head examined or this is worng

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Discussion Overview

The discussion revolves around a specific arithmetic problem involving rounding and the order of operations in a physics context. Participants are exploring the correct approach to solving the expression -9.300 + 2.4 * 3.21 and addressing confusion regarding the expected answer.

Discussion Character

  • Homework-related, Technical explanation, Debate/contested

Main Points Raised

  • One participant expresses confusion over the arithmetic problem, initially arriving at -22.149 instead of the expected -1.6.
  • Another participant suggests that the confusion may stem from incorrectly subtracting instead of adding.
  • A later reply indicates that mistakes were made in both the sign and the order of operations, leading to incorrect results.
  • Participants discuss the importance of following the order of operations, noting that failing to do so can lead to significant errors in calculations.
  • There is mention of a mnemonic for remembering the order of operations, although its application is debated among participants.
  • Some participants acknowledge making similar mistakes and share their experiences with the problem.
  • One participant humorously suggests that everyone might be going insane due to the confusion surrounding the problem.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the correct approach to the problem, as multiple interpretations of the order of operations and arithmetic errors are discussed. Disagreement exists regarding the nature of the mistakes made and the implications of those mistakes.

Contextual Notes

Participants highlight the need to adhere to the order of operations, but there is no resolution on the specific arithmetic errors made. The discussion reflects varying levels of understanding and interpretation of the problem.

Who May Find This Useful

This discussion may be useful for students learning about arithmetic operations, rounding, and the order of operations in mathematics, particularly in a physics context.

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http://library.thinkquest.org/10796/ch1/ch1.htm

I have some down time for the next 3 months and figured I might as well do something constructive and teach myself physics.

I am doing so on thee above website, but question 2 on section 3 has me stumped.

This section is about when and how to properly round, but I am baffled.

Question: -9.300 + 2.4 * 3.21

I am getting -22.149 which properly rounded would be -22, but they are saying it is -1.6

This just can't be right

If you put the wrong answer in enough times it will give you the correct answer.

Thank you in advance for all help.
 
Last edited by a moderator:
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If you are getting -22 you have subtracted the result of multiplication instead of adding it.
 
Would you like us to suggest a good psychiatrist?

I finally got -22.149 but I had to make two mistakes.

1: replace the "+" by "-" as Borek suggests and
2: (far worse) not abide by the "order of operations" and do (-9.300- 2.4)*3.21.
 
Last edited by a moderator:
Wow, once I spotted the sign problem I was not digging deeper
 
You only need to make the "reordering the operations" mistake to get -22.149 since (-9.300+2.4)*3.21=-22.149. To sakartelephon, you cannot just do individual computations from left to right; you must first order your computations based on the type of operation. The order of operations, from first to last, is parentheses, exponents, multiplication/division, addition/subtraction (the standard mnemonic to remember this is "please excuse my dear Aunt Sally"); this is more thoroughly explained at http://en.wikipedia.org/wiki/Order_of_operations . For -9.300+2.4*3.21, we must first multiply 2.4 and 3.21 to get 7.70400, and then add -9.300 and 7.70400 to get -1.59600.
 
Borek said:
Wow, once I spotted the sign problem I was not digging deeper
I'm just better than you at making mistakes!:biggrin:
 
You did the addition before the multiplication.
Lots of beginning students do that.
3 plus 4 times 2 is either 14 or 24 depending on whether it is 7 times 2 or 3 times 8.

HallsofIvy's mistake is even worse, he should have got more negative than -30 !
Borek was wrong also!
 
rmeade said:
3 plus 4 times 2 is either 14 or 24 depending on whether it is 7 times 2 or 3 times 8.


I think we all must be going insane!

For 3 plus 4 times 2

I get 14 or 11
 
looks likes going to be 3 tough months
 

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