How many coins were there in the box ?

Question

In a guess game , five friends had to guess the exact numbers of coins in a box.
Friends guessed as 31 , 35, 39 , 49 , 37, but none of guess was right. The guesses were off by 1, 9, 5, 3, and 9 (in a random order).

Can you determine the number of coins in a box ?

Answer 1

There were 40 coind in the Box.
Such as
31 + 9 = 40
35 + 5 = 40
39 + 1 = 40
49 - 9 = 40
37 + 3 = 40

Answer 2

I think answer should be 40

Answer 3

Number of coins =40

39+1
31+9
35+5
37+3
49-9