Saturday, May 3, 2014

Math POTW #29 - Traffic Flow

This question reminds me of genetics/Mendelian inheritance word problems (Punnett Squares). 

7 comments:

  1. I think the total percentage might be 45%
    If 40% of the traffic contained 2+ people, than 60% contained only 1.
    Out of that 60%, 25%, or 1/4 was male, leaving 75%, or 3/4 to be female.
    The question is asking for 75% of 60% in a nutshell.
    If you take a simpler example, 50% of 50% would be 25% of 100%, and that's basically just finding 50% of 50. So 75% of 60% is 45%, which should also represent the percentage of one woman and no man on a car out of all the traffic.

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  2. Yello mates
    So here's how I got the answer

    First I found out how much cars are in total. 32 cars on the busy highway.

    Now I have to find out how much cars contain two or more people (40% of the total cars). The reason why I did this first is because if you try finding how much cars contain 1 person first, you will get da wrong answer because if you read the question carefully, It says "Of those cars containing only one person" so you have to focus on the amount of cars that only have 1 person to get the answer, but to do that, you have to find the amount of cars which has two or more people and subtract it from the total cars

    0.40 x 32 = 12.8. This represents cars with two or more people
    Since you can't have 12.8 cars, I changed it to 12 cars in total. The reason why I rounded it down instead of up is because if you round it up to 13, it doesn't make any sense, You don't have 13 full cars, only 12.8, so 12 cars will make more sense.

    Now we have to subtract the total cars with the cars with two or more people
    32 - 12 = 20
    \ \
    total cars with
    cars two or more people
    20 represents the total amount of cars that have one person inside

    So what we have to do now is find out how much humans inside the cars are dudes
    To do that we have to do 0.25 x 20 = 5

    5 represents cars that only have males
    Now we subtract it from the total amount cars that have one person
    20 - 5 = 15
    To check I did: 25% of 20 is 5 and 75% of 20 is 15
    15 females equals 75%
    Yay we are done right? nawwww
    If you read the question properly it say find the percentage of ALL the cars which contained exactly one female and no male.

    So what we do now is 15 ÷ 32 = 0.46
    \ \
    Cars with Total cars
    females
    0.46 x 100 = 46%

    So I think that 46% of the total cars are only females
    That is all,
    Bye!!! Lads

    ReplyDelete
    Replies
    1. good try! John~ going with concrete numbers (total cars) is a good strategies; however, the rounding up/down sometimes may impact the percentage, especially when the sample size is small (ie. your sample size is 32). Where did you get the sample size from anyway? did you count the cars in the illustration? =) funny how I never even considered that; i saw it as just a colourful picture getting our minds around the question... =)

      good work~

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  3. Hello readers!
    This is how I solved the problem of the week above.
    First, while reading the problem, I jotted down a note to help me get started.
    40% = 2+ people
    I subtracted 40% from 100% which is 60%. This means 60% = 1 person/car.
    In the question it said 25% was male. So, out of 60%, 25 of it went to males. This means the rest of it must go to females.
    I subtracted 25 from 60. 60 - 25=35. This means 35% was females.
    Therefore, the percentage of cars that contained exactly one female and no males was 35%.
    Thank you for your time!
    BYE!

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    Replies
    1. hi Krupa, good try! your first assumption is correct (re: 60% w/ one driver)
      however, the second part of the question essentially is asking "what is 75% of 60%?". you now have to see 60% as a 'whole' (cars with one driver)..... see Emily's explanation above~ cheers!

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  4. 100-40=60
    60/4=15
    15*3=45
    45% of cars had only one female in them

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  5. 45% was the correct answer. Do you see why?

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