At exactly what time past 9:00 will the minute and hour hands of an accurate working clock be precisely perpendicular to each other for the first time? Options:	A) 20 13/21 minutes past 7:00	B) 20 13/17 minutes past 9:00	C) 21 3/23 minutes past 7:00	D) 21 9/11 minutes past 7:00	E) 22 4/9 minutes past 7:00
A1 = hour angle   A2 = minute angle   A1-A2 = 90   Assume the minutes = M   A1 = (9*60+M)/12*60 )*360   A2 = M*360/60   Solving all three equation , results in the answer 20 13/17 minutes past 9:00
<result>B</result>
At exactly what time past 9:00 will the minute and hour hands of an accurate working clock be precisely perpendicular to each other for the first time?