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匿名 發問於 科學及數學數學 · 5 年 前

maths

Mr.Tang deposited $10000 in a bank at the beginning of 2012 and $9000 at the beginning of 2013. The interest was compounded yearly at r% p.a. , and total amount he received at the beginning of 2014 was $22000. Find r.

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  • 5 年 前
    最佳解答

    Mr.Tang deposited $10000 in a bank at thebeginning of 2012 and $9000 at the

    beginning of 2013. The interest was compounded yearly at r% p.a. , and total

    amount he received at the beginning of 2014 was $22000. Find r.

    Sol

    10000(1+r/100)^2+9000(1+r/100)=22000

    Set p=1+r/100

    10000p^2+9000p=22000

    10p^2+9p-22=0

    (10p-11)(p+2)=0

    p=11/10 or p=-2(reject)

    r/100=1/10

    r=10

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