A decorator bought a bolt of defective cloth that he judged to be
usable, in which ease the cost would be $0.80 per usable yard. If it was later found that only
of the bolt could be used, what was the actual cost per usable yard

单项选择题A certain clock marks every hour by striking a number of times equal to the hour and the time required for a stroke is exactly equal to the time interval between strokes. At 6:00 the time lapse between the beginning of the first stroke and the end of the last stroke is 22 seconds. At 12:00, how many seconds elapse between the beginning of the first stroke and the end of the last stroke ？（）

A．72
B．50
C．48
D．46
E．44

单项选择题A family made a down payment of $75 and borrowed the balance on a set of encyclopedias that cost $400. The balance with interest was paid in 23 monthly payments of $16 each and a final payment of $9. The amount of interest paid was what percent of the amount borrowed ？（）

A．6%
B．12%
C．14%
D．16%
E．20%