Math doesn't know music

Ouuhhh someone is bad at maths @shiftingsands :D

No, this is how is did it.
P = 3T (120 = 40)
So if P = 60, then T = 20.
(less players = less time to complete). Otherwise what would the equation be?

And I did maths for GCSE and AS Level so...

So if it took 120 people 40 hours to build a house, how long would it take 60 people to build a house...?

House building takes more effort than a concert

Just imagine it in a simpler equation. There's a task, and you're two persons to complete it. Now take away half of them, so only you to do the very same task. Naturally it will take you twice as long as with a friend.