Results 1 to 3 of 3

Math Help - Need Help Quick

  1. #1
    uploader145
    Guest

    Need Help Quick

    it is not the hardest puzzle but I need to know a way to figure it out without doing 50 sums, the most important thing is the way it's figured out and no really hard math answers!

    You are washing up for your mum everyday, on the first day you make 1p, on the next day 2p on the next day 4p, so the amount you get is doubled everyday, so the day after it would be 8p then 16p etc

    how much do you earn in 1 week, 2 weeks, 3 weeks and one month, remember I need to know how it is done and simplely like using powers of and stuff.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Newbie
    Joined
    Sep 2007
    Posts
    2
    First day you get 1 cent (2^0)
    2nd day you get 2 cents (2^1)
    3rd day you get 4 cents (2^2)
    .
    .
    .
    8th day (which is one week later from the first day) you get (2^7) cents
    .
    .
    .
    etc etc etc
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Super Member

    Joined
    May 2006
    From
    Lexington, MA (USA)
    Posts
    11,706
    Thanks
    625
    Hello, uploader145!

    You are washing up for your mum everyday.
    On the first day you make 1p, on the next day 2p, on the next day 4p,
    so the amount you get is doubled everyday.
    So the day after it would be 8p, then 16p, etc.

    How much do you earn in 1 week? .2 weeks? .3 weeks? .one month?

    On successive days you earn: .1, 2, 4, 8, 16, 32, ...

    By the n^{th} day, you've earned a total of:
    . . S_n \;=\;1 + 2 + 2^2 + 2^3 + \cdots + 2^{n-1}

    This is a geometric series with: first term a = 1, common ratio r= 2, and n terms.

    Its sum is: . S_n \;=\;1\cdot\frac{2^n-1}{2 -1} \;=\;2^n - 1


    One week: . S_7 \;=\;2^7 - 1 \;=\;127\,p

    Two weeks: . S_{14} \;=\;2^{14}-1 \;=\;16,383\,p . . . . etc.

    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Just a quick one...
    Posted in the Trigonometry Forum
    Replies: 2
    Last Post: December 5th 2009, 05:54 PM
  2. Help me quick
    Posted in the Algebra Forum
    Replies: 1
    Last Post: June 16th 2009, 02:09 PM
  3. need some quick help
    Posted in the Algebra Forum
    Replies: 1
    Last Post: January 18th 2008, 02:56 PM
  4. How many squares? quick quick quick!
    Posted in the Math Challenge Problems Forum
    Replies: 8
    Last Post: December 10th 2007, 08:11 PM
  5. Quick's quick question
    Posted in the Number Theory Forum
    Replies: 22
    Last Post: July 9th 2006, 04:38 PM

Search Tags


/mathhelpforum @mathhelpforum