How long will it take to complete a task given that 3 workers can compete the same task in 10 days

Well that depends on how many ppl get the task. Example, if 1 person got the task, then you take 10 and divide it by 3.

Hmm, 3 workrs do the task in 10 days
each worker does 1/3 of the work
each day, 1 worker does 1/30 of the work

taskcompleted=1
taskprogress=work times time times number of workers
1=1/30 times time times number of workers

if we say w=number of workers and t=time in days then
1=1/30 times t times w
1=tw/30
if we want to solve for t
multiply both sides by 30/w
30/w=t

it would take 30/w days to complete the task if you have w workers