Need 4th grade math help please! ASAP

[Disney1fan2002]

We are all stumped, including my DH, who is a math whiz. The math problems are called broken calculator. He can use a calculator, but one key is broken, so he can't use that key to find the answer.

Simple enough, right? Well, here is a problem

68 + x = 413

Guess what the broken key is? The - sign. So He can't subtract 68 from 413 to get the answer. How else is he supposed to get the answer? Anyone?

 

[The Mystery Machine]

A math whiz? I solved that without using a calculator and I stink at math.

 

[dizchick]

This is just a guess, but what if you multiplied each side by -1? That way you'd be adding 68 to -413.

68+x=413

(-1)(68 + x) = (-1)(413)
-68-x=-413
-x=-413+68
-x=-345

Then wouldn't the negatives cancel each other out and you'd have x=345. There's a big chance I did this wrong, but just trying to help!

 

[Disney1fan2002]

A math whiz? I solved that without using a calculator and I stink at math.

Can you please tell me what you did so I can get an idea on how to help him? Maybe it is something basic, but my brain is shut off this morning and I know it is going to be a "DOH" moment.

 

[blana]

As a spin off of the above, so long as the negative button still "works", he can do 413 + (-68) = 345

 

[Disney1fan2002]

This is just a guess, but what if you multiplied each side by -1? That way you'd be adding 68 to -413.

68+x=413

(-1)(68 + x) = (-1)(413)
-68-x=-413
-x=-413+68
-x=-345

Then wouldn't the negatives cancel each other out and you'd have x=345. There's a big chance I did this wrong, but just trying to help!

Thanks for that idea, but since it is 4th grade, I don't think algebra is the answer. They have no concept of algebra. Plus in order to enter a negative you need the - key, and that's broken!

 

[Disney1fan2002]

As a spin off of the above, so long as the negative button still "works", he can do 413 + (-68) = 345

The negative button is broken so he can't use it at all. Thanks for the idea though.

 

[The Mystery Machine]

Can you please tell me what you did so I can get an idea on how to help him? Maybe it is something basic, but my brain is shut off this morning and I know it is going to be a "DOH" moment.

Like I said, I stink at 4th grade math. I know the answer but I would not know how to show an equation for the teacher.

I would just subtract 413 from 68 to get X. Maybe someone else can help you better than me.

Oh I see...the "negative button is broken"....got it. Have to think about that.

 

[swanmom]

Can you use 'successive' estimation and the + key to keep getting closer to the answer until you hit it? Sort of like this:

68 + 100 = 168
168 + 100 = 268
268 + 100 = 368
368 + 10 = 378
378 + 10 = 388
388 + 10 = 398
398 + 10 = 408
408 + 1 = 409
409 + 1 = 410
410 + 1 = 411
411 + 1 = 412
412 + 1 + 413

Then add up the red numbers 100 + 100 + 100 + 10 + 10 + 10 +10 + 1 + 1 + 1 + 1 + 1 = 345 !

 

[dizchick]

Haha, yeah come to think of it, that would be a little advanced for 4th grade. So can he not use the subtract key or the negative sign key?

 

[Disney1fan2002]

Like I said, I stink at 4th grade math. I know the answer but I would not know how to show an equation for the teacher.

I would just subtract 413 from 68 to get X. Maybe someone else can help you better than me.

Oh I see...the "negative button is broken"....got it. Have to think about that.

LOL! That's what I said to him. I said it's easy, just do the opposite, until I saw the opposite is the key that is broken! It is the same with all the rest of the problems, If it is a multiplication problem, the division key is the "broken" one, ect.

 

[swanmom]

Nevermind..............I was able to edit my earlier post.

 

[The Mystery Machine]

What if you add 345 to the 68?

 

[Quacktatty]

Does your calculator not have a separate +/- key? That's not the same as the subtraction key.

 

[Disney1fan2002]

Can you use 'successive' estimation and the + key to keep getting closer to the answer until you hit it? Sort of like this:

68 + 100 = 168
168 + 100 = 268
268 + 100 = 368
368 + 10 = 378
378 + 10 = 388
388 + 10 = 398
398 + 10 = 408
408 + 1 = 409
409 + 1 = 410
410 + 1 = 411
411 + 1 = 412
412 + 1 + 413

Then add up the red numbers 100 + 100 + 100 + 10 + 10 + 10 +10 + 1 + 1 + 1 + 1 + 1 = 345 !

Thanks! I think you have it, I am just having him use bigger numbers.

 

[maelstrom]

It's a good thing that I don't have kids and don't ever want kids, because I'd write on the assignment something to the effect of, "obtained new calculator which isn't broken".

 

[Disney1fan2002]

It's a good thing that I don't have kids and don't ever want kids, because I'd write on the assignment something to the effect of, "obtained new calculator which isn't broken".

We figured out the addition and subtraction problems, but the multiplication and division problems..no way. I sent a note in with the homework explaining that we had no clue how to figure it out.

 

[golfgal]

Thanks for that idea, but since it is 4th grade, I don't think algebra is the answer. They have no concept of algebra. Plus in order to enter a negative you need the - key, and that's broken!

Don't be so sure about this. Most schools are teaching basic Algebra as early as 1st grade, they just don't call it that. To me the set up of the problem is very much algebra. Also, the subtract key is not the same as the negative key.

 

[paintnolish]

Don't feel bad. I am routinely stumped by 4th grade math. I am an English major for a reason! Ds is doing negatives, though, and is not in an accelerated math (he takes after his mom!).

 

[swanmom]

Thanks! I think you have it, I am just having him use bigger numbers.

Whooo Hooo !!! I think that's the first time in my life I've figured out something 'math' related! Not a bad start to my day. Glad I could help!