The average (arithmetic mean) length per film for a group of 25 films is s minutes. If a film that runs for 70 minutes is removed from the group and replaced by one that runs for 50 minutes, what is the average length per film, in minutes, for the new group of films, in terms of s?
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Thank for sharing!
this pattern comes up frequently
Can you explain more?
thanks for the answer
thanks, this one was pretty straightforward once you realize the total change is just 20 minutes spread over 25 films
yeah the trade is a net loss of 20, so dividing by 25 gives the per-film drop
ah that's the part i missed, kept trying to use the 70 and 50 separately
wait why is it B and not E? i got confused with the 20 minutes
because the 20 minutes is total across all 25 films, not per film. so you divide by 25
solid 505-555 question, nothing tricky just have to remember it's per film
is the answer E? cuz it decreased by 20?
no, it decreased by 20 total minutes but that's split across 25 films so it's smaller than that
What it tests
Your ability to manipulate linear and quadratic expressions, substitute unknowns, and solve equations under time pressure.
Common trap
Losing a sign when moving terms across the equals sign, or dividing both sides by a variable that could equal zero.