Oh, an interesting story related to this question, after the paper, I asked a lady how she solved this question, she was saying by allocating the weight according to data given, she said that although, it consumed my 15 minutes but my answer was correct. And I was shocked her descending order of weight was absolutely correct.This is said to be a presence of mind.
About me,
(alhamdollilah, my majority of questions are also correct, though objective created problem for me)
And my folly, I did know the formula of range, but in hustle bustle I have not attempted.