- Joined
- Jan 5, 2016

- Messages
- 53

- Reaction score
- 13

*first question states something like:*

**average speed of skater down hill is 23 mph.**

for the first 1/3 of the hill, average speed was 17 mph

the average speed of the second 1/3 was 15 mph.

..what was the skier's average speed for the final 1/3 of the journey?

for the first 1/3 of the hill, average speed was 17 mph

the average speed of the second 1/3 was 15 mph.

..what was the skier's average speed for the final 1/3 of the journey?

for this question, it could be solved by doing this and solving for x.

(17 + 15 + x)/3 = 23

*the next question states something like this:*

**a driver drives halfway to the airport, a distance of 30 miles, going 50 mph.**

how fast must he go for the second 30 miles of the drive in order to meet an average speed of 60 mph?

how fast must he go for the second 30 miles of the drive in order to meet an average speed of 60 mph?

for this one, i also tried

(50 + x)/2 = 60 .. i got 70, but the answer is 75.

To solve the second question, apparently we had to take in account of the time traveled at 50mph.

lol, my question is: what's the difference between these two problems -- why did we have to consider time in the second question, but not the first question? (i figured averaging the speeds were fine for these questions because the distances of each period in the question were the same -- aka, 1/3 distance in the first question, and 30 miles in the second question)