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Math

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Can you help me with this problem?

At the beginning of January, Lisa had some money in her savings account. Each month she was able to deposit enough from her allowance to double the amount currently in the account. However, she had a loan to pay off, requiring her to withdraw $10 from the account monthly. At the end of May, she had $2 left in the account. How much did Lisa have at the beginning of January?

  • Math -

    At the beginning of January, Lisa had some money in her savings account. Each month she was able to deposit enough from her allowance to double the amount currently in the account. However, she had a loan to pay off, requiring her to withdraw $10 from the account monthly. At the end of May, she had $2 left in the account. How much did Lisa have at the beginning of January?

    It depends on when the money was doubled, before or after the $10.00 was paid out.
    One way:
    Jan.1--$X
    Feb.1--$2X - 10
    Mar.1--$(4X - 20) - 10 = (4X - 30)
    Apr.1--$(8X - 60) - 10 = (8X - 70)
    May 1--$(16X - 140) - 10 = (16X - 150)

    16X - 150 = 2 or X = $9.50

    The other way:
    Jan.1--$X
    Feb.1--$(X - 10)2
    Mar.1--$[(X - 10)2 - 10]2
    Apr.1--I'll let you finish this one.

    Jan.1st $X
    Feb.1st 2X - 10
    Mar.1st

  • Math -

    thanks

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