Subtraction

[louise1]

Hello -

Can you help me with this math problem?

Place two subtraction signs between theses digits to give the correct answer:
3 8 7 9 = 22

I tried 3 - 8 + (-7) + 9 = but I think this equals 21.

I also tried other ways to solve this problem and asked someone else. Can you get me going in the right direction? Any help is appreciated.

 

[Romsek]

You've included an addition (+) sign. Two of them in fact!
Problem states insert two subtraction signs. That is all.

Try again. (hint: it's not really that difficult)

 

[tkhunny]

There aren't that many ways to put just two subtraction signs (and one addition?).

3 - 8 - 7 + 9
3 - 8 + 7 - 9
3 + 8 - 7 - 9

That's it.

3 - 8 - 7 + 9 = -5 - 7 + 9 = -12 + 9 = -3
3 - 8 + 7 - 9 = -5 + 7 - 9 = 2 - 9 = -7
3 + 8 - 7 - 9 = 11 - 7 - 9 = 4 - 9 = -5

As for your attempt:

3 - 8 + (-7) + 9 = -5 - 7 + 9 = -12 + 9 = -3 -- And we already showed that outcome.

Since this isn't making any sense, I have to wonder if we actually have the right problem statement. Do we get parentheses? Can we use -3 out front, even though that isn't "between"? The full and original wording is important.

 

[firemath]

Only two subtraction signs and (Hint) None are on the right..

Spoiler (don't look until you've solved it) [MATH]38-7-9=22[/MATH].

 

[louise1]

Thank you. I need to think more expansively about possibilities, clearly. I really appreciate the constructive feedback and math help. I am grateful.

 

[tkhunny]

Thank you. I need to think more expansively about possibilities, clearly. I really appreciate the constructive feedback and math help. I am grateful.

Expansively? I can't object to that, but it may require less expansively as the author may just want you to do something silly that they thought was awesome when they wrote a textbook.

Not really happy about that solution.

To make "3" and "8" into 38, one must multiply, 3 * 10 = 30 and add 30+8. That is not "insert two subtraction signs". So hard to write a good problem. {shakes head}