Patty ran a marathon at an average speed of 3 mph for some time and then at an average speed of 6 mph for the rest of the marathon. If she made no stops during the run and her average speed for the entire marathon was 5 mph, for what fraction of the total time did she run at 3 mph?  Choose the correct answer:	A) 1 / 5	B) 2 / 3	C) 2 / 5	D) 3 / 5	E) 1 / 3

Rationale: we do n ' t need to get into calculations for solving this question . we can use the concept of weighted averages . we know that if the average speed for the entire marathon was 5 mph , she ran at 6 mph for a longer duration . 2 1 3 - - 5 - - - - 6 this shows that you can divide the entire journey in 3 equal parts . thus , 2 / 3 part she ran at 6 mph and 1 / 3 part she ran at 3 mph . answer : e
Answer: E