Q: There are 235 books in a library. On Tuesday, 227 books are taken out. On Thursday, 56 books are brought back and 35 books are taken out again on Friday. How many books are there now?
A: On Tuesday, 227 books were taken, so there are 235 - 227 = 8 books left. 56 books were brought back on Thursday, so there are 8 + 56 = 64 books in the library. Finally, 35 books are taken out on Friday, leaving 64 - 35 = 29 books available. The answer is 29.

Q: Gail has some bills in her wallet which amount to $100. She has four $5 bills and three $20 bills, and the rest are $10 bills. How many $10 bills are in her wallet?
A: Four $5 bills amount to $5 x 4 = $20. Three $20 bills amount to $20 x 3 = $60. So Gail's $5 and $20 bills amount to $20 + $60 = $80. Thus, her $10 bills amount to $100 - $80 = $20. Therefore, she has $20 / $10 = 2 $10 bills. The answer is 2.

Q: The number of short students in a class is 2/5 of the total number of students. If there are 90 tall students, and the class has 400 students, calculate the total number of students with average height.
A:
The number of short students in the class is 2 / 5 * 400 = 160. The total number of short and tall students is 160 + 90 = 250. Since there are 400 students in the class, the number of students with average height is 400 - 250 = 150. The answer is 150.