中文看多了，理解英文有问题，发几道做错过的英文数学题

还有自己想出来的一个变体：
If x and y are positive integers and , what is the value of  x+y?
(1)1+x+y+xy=15
(2)x^2-4=0

求答案。

都是些老题，挺经典的。
1.In a stack of boards at a lumber yard, the 20th board counting from the top of the stack is immediately below the 16th board counting from the bottom of the stack.  How many boards are in the stack?
(A) 38
(B) 36
(C) 35
(D) 34
(E) 32



161. Beginning in January of last year, Carl made deposits of $120 into his account on the 15th of each month for several consecutive months and then made withdrawals of $50 from the account on the 15th of each of the remaining months of last year. There were no other transactions in the account last year. If the closing balance of Carl’s account for May of last year was $2,600, what was the range of the monthly closing balances of Carl’s account last year?
(1) Last year the closing balance of Carl’s account
for April was less than $2,625.
(2) Last year the closing balance of Carl’s account
for June was less than $2,675.

123. Joanna bought only $0.15 stamps and $0.29 stamps.
How many $0.15 stamps did she buy?
(1) She bought $4.40 worth of stamps.
(2) She bought an equal number of $0.15 stamps
and $0.29 stamps.


48. In June 1989, what was the ratio of the number of
sales transactions made by Salesperson X to the
number of sales transactions made by Salesperson Y ?
(1) In June 1989, Salesperson X made 50 percent
more sales transactions than Salesperson Y did
in May 1989.
(2) In June 1989, Salesperson Y made 25 percent
more sales transactions than in May 1989.

10 teachers，男女都有，随机挑出2人作某事，问两个都是女老师的概率>1/2吗？
(1)女老师的人数>5  
(2)两个都是男老师的概率<1/30