Multiple choice

A bag contains 6 red balls and 4 blue balls. One red ball weighs 0.35 kg and one blue ball weighs 0.25 kg. How many blue balls are added to the bag, if the average weight decreased by 0.02 kg?

  1. 2

  2. 3

  3. 4

  4. 5
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Initial average weight = (6×0.35+4×0.25)/10 = 3.1/10 = 0.31 kg. After adding x blue balls: average = (3.1+0.25x)/(10+x) = 0.29. Solving: 3.1+0.25x = 2.9+0.29x, so 0.04x = 0.2, x = 5.

Keep practicing — related questions