1．The Centerville Middle School chess team consists of two boys and three girls.A photographer wants to take a picture of the team to appear in the local newspaper.She decides to have them sit in a row with a boy at each end and the three girls in the middle.How many such arrangements are possible？（　?。?br />Centerville中學(xué)的國際象棋隊由兩個男孩和三個女孩組成。一名攝影師想為當(dāng)?shù)貓蠹埮臄z這個團隊的照片。她決定讓他們坐成一排，兩端各坐一個男孩，中間是三個女孩。這樣的排列有多少種可能性？（　?。?/div>

2．There are 81 grid points（uniformly spaced） in the square shown in the diagram below,including the points on the edges.Point P is the center of the square.Given that point Q is randomly chosen from among the other 80 points,what is the probability that the line PQ is a line of symmetry for the square？（　?。?br />如圖所示的正方形內(nèi)有81個網(wǎng)格點（均勻分布），包括邊緣上的點。點P是正方形的中心。若從其他80個點中隨機選擇定點Q，那么線PQ是正方形的對稱線的概率是多少？（　?。?/div>

3．Each of two boxes contains three chips numbered 1，2，3.A chip is drawn randomly from each box and the numbers on the two chips are multiplied.What is the probability that their product is even？（　?。?br />兩個盒子中的每一個都包含編號為1，2，3的三個籌碼。從每個盒子中隨機抽取一個籌碼，然后將兩個籌碼上的數(shù)字相乘。他們的乘積是偶數(shù)的概率是多少？（　　）