Elias and niko are polishing the silver at the heritage museum. elias could polish all the silver himself in 40 minutes. that task would take niko 50 minutes to complete alone. whick table is filled in correctly and could be used to determine how long it would take elias and niko polished te silver together?

We let x be the number of hours both could the job together.
The fraction of the job done by Elias is
x/40

The fraction of the job done by Niko is
x/50

Together they would be able to finish the job (one job)

x/40 + x/50 = 1
x = 1 / (1/40 + 1/50)
x = 22.22 minutes

The first one, i believe, would be correct. all the others have one thing in common, and that's that they have repeating numbers. in the second one, x and y have repeating 6's and 3's, and in the third, x and y have repeating 6's as well. in the last one, there are repeating 3's. the first one has no repeating numbers.