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Alyssa is enrolled in a public-speaking class. Each week she is required to give a speech of greater length than the speech she gave the week before. The table below show the length of several of her speeches:

WK #/Length of Speech (seconds)
3/150, 4/180, 5/210, 6/240

If this trend continues, in which week will she give a 12-minute speech?

Choices are:

By converting 12 minutes to 720 seconds and going week by week, I chose 22.

How do I set this up as a problem and solve it? Thanks

  • math - ,

    each week she increases her speech by 30 seconds
    12 minutes = 720 seconds
    (you are right so far)

    This is an arithmetic sequence, where
    a = 150 , d = 30
    we need to find which term is 720
    150 + (n-1)(30) = 720
    30n - 30 = 570
    30n = 600
    n = 20

    but what I considered first term is really the third term (3rd week)
    so she reaches the 12 minute speech in week 22

    You are right!

  • math - ,

    this answer^ is bull

  • math - ,

    the correct answer is actually Alyssa is a satanist and she will die before the last speech which is 12 minutes...

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