I think this is a fraction? It's: 4 (-2.5) Trying to get the answer

khi200

New member
Joined
Jan 22, 2019
Messages
1
Hi, I've been working on this problem: 4(-2.5) for some time for my homework, but I can't seem to figure out how to get the correct answer. According to a website, the answer to the math question is -10 but it doesn't explain how it got that answer in the first place. I end up getting a different answer than -10 so I'm under the impression that I'm not doing the problem correctly.
I need some help with it. Can someone please explain how I can get the correct answer?

I have a picture of what I've been doing on paper and a screenshot of the website explaining the problem to me.
Feel free to look at it, and give me some feedback and guidance. Thank you all.
 

Attachments

Otis

Senior Member
Joined
Apr 22, 2015
Messages
1,173
2.5 is the decimal form of the mixed number 2½.

2½ = 2 + ½

2.5 = 2.0 + 0.5

0.5 is the decimal form of ½, yes? That is, 0.5 is 5/10, which reduces to ½.


Using your (distributive) approach, we don't multiply 4×5. We multiply 4×0.5

In other words:

(-4)(2.5) = (-4)(2 + 0.5) = (-4)(2) + (-4)(0.5) = (-8) + (-2) = -10


You could also multiply 4×2.5 using longhand multiplication; remember to put a negative sign in front of the result.


You could also switch to rational form, by rewriting 2.5 as an improper fraction and then cancelling the common factor of 2 (before multiplying the two fractions).

\(\displaystyle \dfrac{-4}{1} \cdot \dfrac{5}{2} = \dfrac{-2}{1} \cdot \dfrac{5}{1} = \dfrac{-10}{1}\) :cool:
 

Harry_the_cat

Full Member
Joined
Mar 16, 2016
Messages
950
Hi, I've been working on this problem: 4(-2.5) for some time for my homework, but I can't seem to figure out how to get the correct answer. According to a website, the answer to the math question is -10 but it doesn't explain how it got that answer in the first place. I end up getting a different answer than -10 so I'm under the impression that I'm not doing the problem correctly.
I need some help with it. Can someone please explain how I can get the correct answer?

I have a picture of what I've been doing on paper and a screenshot of the website explaining the problem to me.
Feel free to look at it, and give me some feedback and guidance. Thank you all.
4 x 2.5 = 4 lots of 2.5 = 2.5 + 2.5 +2.5 + 2.5 =10

Therefore 4 x -2.5 = -10
 

topsquark

Full Member
Joined
Aug 27, 2012
Messages
269
Hi, I've been working on this problem: 4(-2.5) for some time for my homework...
A suggestion: When doing Mathematics use fractions not decimals. It's just a good practice to keep.

-Dan
 

Jomo

Elite Member
Joined
Dec 30, 2014
Messages
3,050
Hi, I've been working on this problem: 4(-2.5) for some time for my homework, but I can't seem to figure out how to get the correct answer. According to a website, the answer to the math question is -10 but it doesn't explain how it got that answer in the first place. I end up getting a different answer than -10 so I'm under the impression that I'm not doing the problem correctly.
I need some help with it. Can someone please explain how I can get the correct answer?

I have a picture of what I've been doing on paper and a screenshot of the website explaining the problem to me.
Feel free to look at it, and give me some feedback and guidance. Thank you all.
2.5 = 2.50 so think $2.50. If you buy 4 items that each cost $2.50, then how much do you pay for the items? you really should now this answer, Sure you should know how to compute this by hand and a few methods have been given already. Study them.
 
Top