GMAT/留學申請專業顧問 Donz 之資訊交流園地

  161.
  Beginning in January of last year, Carl made deposits of $120 into his account on the 15th of each month for several consecutive months and then made withdrawals of $50 from the account on the 15th of each of the remaining months of last year. There were no other transactions in the account last year. If the closing balance of Carl’s account for May last year was $2,600, what was the range of the monthly closing balances of Carl’s account last year?
  1)   Last year the closing balance of Carl’s account for April was less than $2,625.
  2)   Last year the closing balance of Carl’s account for June was less than $2,675.
 

Solution:

  按照月份   1    2    3    4    5    6    7    8    9    10    11    12
                                    $2,600

  我們只要知道從哪個月份"開始"提錢就知道了

  條件 1:  四月份金額 < 2625
              四月份只可能有兩個金額 一個是 2,480 (五月存錢)

                                  一個是 2,650 (五月提錢)
               很明顯 四月份的金額是 2,480 所以五月份是存錢的

  條件 2:  六月份金額 < 2625
               六月份只可能有兩個金額 一個是 2,720 (六月存錢)
                                  一個是 2,550 (六月提錢)
           很明顯 四月份的金額是 2,550 代表六月提錢

    兩個條件個別都無法求出哪個月份"開始"提錢
    但合在一起 就知道 五月存錢 六月提錢
    所以我們可以求出 Balance 的 Range

    Answer: (C)