Re: [計量] PP1-DS-90
看板GMAT (GMAT入學考試)作者zacchen (sunny side up)時間17年前 (2007/10/23 10:01)推噓0(0推 0噓 0→)留言0則, 0人參與討論串2/2 (看更多)
※ 引述《rnrn ()》之銘言：
: On Jane's credit card account, the average daily balance for a 30-day billing
: cycle is the average (arithmetic mean) of the daily balances at the end of
: each of the 30 days. At the beginning of a certain 30-day billing cycle,
: Jane's credit card account had a balance of $600. Jane made a payment of
: $300 on the account during the billing cycle. If no other amounts were added
: to or subtracted from the account during the billing cycle, what was the
: average daily balance on Jane's account for the billing cycle?
: (1) Jane's payment was credited on the 21st day of the billing cycle.
: (2) The average daily balance through the 25th day of the billing cycle was
: $540.
: 答案是(D) 請幫我解答 謝謝^^
選項一
300塊在第21天入賬
所以第一到第20天的balance是600,第21天到第30天的balance是300
平均就可以算的出來
選項二
設balance為600的天數為x,balance為300的天數為y
解聯立
(600x+300y)/25=540
x+y=25
得出x=20, y=5
平均也可以算的出來
以上
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