[Q. ] 兩道數學題
1. There are seven different keys,A,B,C,D,E,F,G ina ring, what's the
probability that A,B are placed together?
A. 1/7
B. 2/7
C. 1/3
D. 1/4
E. 1/5
答案是C,想問我的算法這樣有沒有錯....1-5*4*4*3*2*1/6!
我是先決定A位置...用1扣掉A的左右兩邊不做B的機率這樣算式對嗎??
2.In the correctly worked addition problem shown, where the sum of the
two-digit positive integers AB and BA is the three-digit integer AAC,and
A,B and C are different digits, what is the units digit of the integer AAC?
A. 9
B. 6
C. 3
D. 2
E. 0
答案為E, 這題我是直接湊答案 A=1 B=9,19+91=110, 這題有特別的算法或觀念嗎??
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