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to save fuel on the 240 km trip to the cottage, the Nakamura family reduce their usual average speed by 20 km/h. this lengthens their journey by 1 hour. what is the slower average speed?

pleassee help! thanks :)

  • math - incomplete -

    How long does it usually take them to make this trip?

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    oh my gosh! so my teacher handed us two versions of this question...i didn't have that answer! sorry. the proper question i will repost.

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    never mind it does not say. does this mean the question is complete and unable to answer? its a question on an assignment and i do not know how to answer it. should ijust say uncomplete?

  • math -

    Let V1 = the original average speed and V2 = the slower average speed. You have these two equations in two unknowns:

    V1 - V2 = 20 (km/h)

    240/V2 - 240/V1 = 1 (hour)

    You want to solve for V2. Use substitution, V1 = V2 + 20

    240/V2 -240/(V2 +20) = 1

    240*[1/V2 - 1/(V2+20)] = 1
    20/[V2(V2+20)] = 1/240
    V2*(V2+20) = 4800

    You can solve this as a quadratic equation and take the positive root. You should get

    V2 = 60 km/h

  • math (not incomplete) -

    Note that there was enough information provided to solve for both velocities, using simultaneous equations.

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  • math -

    While this gave me the answer, I was unable to understand how this was done. 2/10 would not math again

  • math -

    Also, shout out to my pears

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