I managed to submit. I confused the expected result with the result returned by my solution.

Amount of information in this bug report makes it impossible to even start fixing the issue. Closing as per insufficient details.

some test are not matching with the function description make it impossible to submit even the solution passing all the other test Cases

That's because flat is available since Node 11, but this kata is available only in Node 8. flat will work when this kata will be updated to the newer version of Node.

flat method doesn't work here

great solution, i couldn't solve it even after hours trying

this should work, maybe it's a test issue depending on what is the language that you are doing this

pretty similar to my solution

for your problem you shouldn't divide each element by the array length, you should only divide the sum, i had that same problem so it's probably a rounding issue indeed

you can't return a forEach, you probably should use a reduce or just a normal for loop

i think you should make number receive himself + number * percentage... etc