Bob wants to run a mile in the same time as his sister. If Bob’s time for a mile is currently 10 minutes 40 seconds and his sister’s time is currently 5 minutes 20 seconds, by what percent does Bob need to improve his time in order run a mile in the same time as his sister?
Choose the correct answer:	A) 3 %	B) 50 %	C) 8 %	D) 10 %	E) 12 %

Rationale: "bob ' s time = 640 secs . his sis ' time = 320 secs . percent increase needed = ( 640 - 320 / 640 ) * 100 = 320 / 640 * 100 = 50 % . ans ( b ) ."
Answer: B