maths

A shop is sending out a bill for an amount less than #100.the accountant interchange the two digits and so overcharage the customer by #45,given that the sum of the two digits is 9.find how much the bill should be?.thanks

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  1. a + b = 9
    ------------------

    b a - a b = 45

    10 b + a - 10 a - b = 45

    9 b - 9 a = 45

    b - a = 5
    -----------------------
    so
    +a + b = 9
    -a + b = 5
    ____________ add
    2 b = 14
    b = 7
    then a = 2
    so maybe 27 or 72?
    well he overcharged by 45
    so I suppose it should have been 27 and he chargesd 72

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  2. how did u got 27 and 72 i don,t understand

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  3. the number is a b or b a

    b = 7 and a = 2
    so
    7 2 or 2 7

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