Let average weight of 25 persons be X
Average=(sum of weights of 25 persons)/25
that is (sum of weights of 24 persons+weight of man going) is =25X-----------------------------(1)
increase in Average Weight = X+1
New Average = (sum of weight of 25 persons)/25
X+1=Sum of weight of 25 person/25
(sum of weight of 24 person+70) = 25(X+1)----------------------------------------(2)
25(X+1)-70=25X-weight of person going
Weight of person going =70-25=45