[問題]請教2題

[yuga]

1. On week a certain truck rental lot had a total of 20 trucks, all of which were on the lot Monday morning. If 50 percent of the trucks that were rented out during the week were returned to the lot on or before Saturday morning of the week, and if there were at least 12 trucks on the lot that Saturday morning, what is the greatest number of different trucks that could have been rented out during the week?

ANS:16

2. How many positive integers less than 20 are either a multiple of 2, an odd multiple of 9, or the sum of a positive multiple of 2 and positivie multiple of 9?

ANS:15

與其說不會算，我看是題目根本讀不懂 ，請大家幫助我，感恩!

[simonyu]

無聊逛進來的，才發現RE跟AT的題目怎麼那麼像？根本就是一樣嘛～

1.題目問說，如果星期一有20台車，本週裡租出去的車至少要有50%在星期六之前或當天回來，問在星期六有12台車出現，本週內租出去的車子最多可能有幾台？

假設租出去x台，應回來的加上沒租出去的要等於出現的，所以可得0.5x+(20-x)=12，x=16

2.題目問小於20的正整數中，符合下列條件之一者(1)2的倍數(2)9的奇倍數(3)2的正倍數和9的正倍數和，共有幾個？
1)2的倍數...共有9個
2)9的奇倍數...只有1個(9)
3)2的正倍數和9的正倍數和...有5個(11,13,15,17,19)

因為彼此都沒有交集，所以個數直接加起來即可，9+1+5=15個