1. 從1,2,...,100中, 最少要選出多少個整數,才能確保有2個的個位數字相同?
2. 當123456789除以18時, 餘數是多少
3. a day is said to be"good" if the product of the "month" and the "day" is a composite no. EG.: since 1x27=27 and 27 is a composite no., we say that 27th Jan is a "good day". How many good days are there in the year2007?
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好好玩既Maths
2007-11-28 10:18 am
回答 (1)
2007-11-28 11:00 am
✔ 最佳答案
1. 個位數字共有十個可能性, 所以最少要選出十一個整數,才能確保有2個的個位數字相同.2. 123456789 , 所有數字加起來是45, 所以這數是能夠被9 整除而同時是單數. 所以餘數是9.
3. Non good days = non composite no. = prime number day in Jan = (1,2,3,5,7,11,13,17,19,23,29) of Jan ( for other months, any days are good days, because the product of month and day must be composite number)
所以 no. of good days = 365 - 11 = 354
參考: me
收錄日期: 2021-04-13 14:36:18
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