A weight lifter lifts 400 lbs on his fifth attempt, thereby increasing his average by 5 lbs. What is his average after the fifth attempt?

Question

anonymous · Answer

The average μ for his first 4 attempts is: μ = (x + x + x + x)/4 = 4x/4 = x = μ

The average after the fifth lift is (x + x + x + x + 400)/5 = (4x + 400)/5 = x + 5 = μ + 5

 So obviously Sx after the 5th lift was 25 lb more than Sx after the first 4.

 So the average for the first 4 was 375 lb each.

 And his average after the fifth attempt is 
 375 x 4 =1500
 400 x 1= ..400
 ----------------------
 So μ = 1900/5 = 380 lb.

 Answer: The average after the fifth attempt was 380 lb