Question 23781
First number = f
second number = s
Third = number = t
fourth number = n


f = s-20 ---------------> s-f=20
t = 1 + 2s-40 ----------> 2s-t=39
n = 5 + 2s-40 ----------> 2s-n=35


s-20+s = 2s-39+2s-35 (sum of all numbers) -------> -2s = -54


                        Hence s = 27 (second number)

(27)-f = 20 ---------> s-f=20
f=7 (first number)


2(27)-t=39 --------->2s-t=39
54-t=39 
t=15 (third number)


2(27)-n=35 --------->2s-n=25
54-n=35
n=19 Fourth number 


to check first number + second number = third number + fourth number
27+7 = 19+15
34=34


Hence, the four numbers are 27, 7, 15 and 19.
Paul.