[Solved] Why would (40 + 2*5)*1.1 output 55.0000...01 in Python?

Question

n = int(input())
tcost = (40 + 5*n)*1.1
print(tcost)

input 2 and you get:

2
55.00000000000001

[Program finished]

EDIT: Sorry for the title typo (was 50.00...01 earlier)
https://code.sololearn.com/cO7g469R7nle/?ref=app

Answer 1

Its a rounding error due to the way a computer processes data. (Truncation Error)
In this specific code, the computer uses a series addition numerical method to solve power to 1.1
Use math libraries to solve for exponents or use string manupulation to restrict (round) your answer

print("%.2f" % tcost)

Or

print(round(tcost, 2))

Answer 2

Not sure if this would work, but try changing 40 and 5 to 40.0 and 5.0 respectively, and make n floating point instead of int

Answer 3

Leonardo Amaro Thanks, I will do that but lol this is weird

Update: output's the same

Answer 4

https://docs.python.org/3/tutorial/floatingpoint.html

Says due to the approximations made to translate human decimal system to computer's binary system vice versa, aka base2 <-> base 10 equivalence

so it has to do with how computers compute rather than python.

(typed 0.00000000000001 and added python and got a reddit page that linked to this, I just couldn't find a phrasing to search about it other than this and didn't think I'd get a result at all, so I am sorry, but I hope that it'll at least turn out useful)

Answer 5

Areeb Qureshi Thanks a bunch about the information, I wouldn't know how to search about it.

It's not the power operator that I used but simply multiplication. I'm guessing it's the same error by name, though. Either way, very good to know!

I did use round later on btw :-)