susan asked in 教育與參考考試 · 1 decade ago

一題機率問題,一題三角型問題,一題加法問題

Q2: The sum of the first k positive integers is equal to k(k+1)/2. What is the sum of the integers from n to m, inclusive , where 0<n<m?

答案是:m(m+1)/2-(n-1)n/2

答案為什麼有減號???

題目是問sum, n(n+1)/2+m(m+1)/2

請幫忙解說詳細謝謝!!

Q3: In triangle ABC, point X is the midpoint of side AC and point Y is the midpoint of side BC. If point R is the midpoint of line segment XC and if point S is the midpoint of line segment YC, what is the area of triangular region RCS ?

條件1: The area of triangular region ABX is 32.

條件2: The length of one of the altitudes of triangle ABC is18

答案是:條件1單獨成立。

我不懂耶?? 我RCS圖形劃出來,跟ABC圖形 不一樣,請指導我一下謝謝。為什麼條件1能成立呀!

Q4: On a certain transatlantic crossing ,20 percent of a ship’s passengers held round-trip tickets and also took their cars abroad the ship. If 60 percent of the passengers with round-trip tickets did not take their cars abroad the ship, what percent of the ship’s passengers held round-trip tickets?

答案是50%

0.6-0.2=0.4

為什麼是50% ,請解說謝謝。

2 Answers

Rating
  • 玉米
    Lv 4
    1 decade ago
    Favorite Answer

    Q2:

    The sum of the first k positive integers is equal to k(k+1)/2

    這段話是解釋k個等加級數總合的為k(k+1)/2

    What is the sum of the integers from n to m, inclusive , where 0<n<m?

    題目要求n~m等加級數總合

    依上式為(m-n+1)*(n+m)/2,m-n+1為數字個數,n+m為首項+末項

    (m-n+1)*(n+m)/2=m(m-n+1)/2+n(m-n+1)/2

    =m(m+1)/2-mn/2+mn/2+n(1-n)/2

    =m(m+1)/2-n(n-1)/2

    Q3:

    △ABC的AC邊的中點為X,BC邊的中點為Y

    XC邊的中點為R,YC邊的中點為S

    △ABC相似△XYC相似△RSC

    BC長=2*YC長,所以△ABC=4△XYC(因為底和高皆為△ABC1/2),同理△XYC=4△RSC

    △ABX=1/2△ABC

    其他的部分好像條件不足

    Q4:

    條件是實際有20%的乘客有票也有開車搭船

    假設60%的乘客有票但沒有開車搭船

    問實際有多少的乘客有票:P(T)

    因為假設60%的乘客有票但沒有開車搭船:P(t&nc)

    所以40%的乘客有票也有開車搭船:P(t&c)

    P(T)*P(t&c)=0.2

    P(T)*0.4=0.2

    P(T)=0.5

    Source(s): ME
  • 1 decade ago

    可不可以把題目翻成中文

    看不懂英文XD

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