i need help with math hw?

Question

i need major help. heres the question...

Flying east between 2 cities, a plane speed is 380 miles/hr. On the return trip it flies at 420 miles/hr. Find the average speed for the round trip.

This is the problem. I know the answers not 400.

Can someone plz help me. And if its not too much, explain how u got ur answer. Thanks.

Answer 1

Distance = 20
Rate = 380

Distance = 20
Rate = 420

D = RT
Time it takes to GO = D/R = 20/380
Time it takes to RETURN = D/R = 20/420

Average speed =
Total Distance / Total Time =
40/(20/380 + 20/420) = 399

You can do it my way because distance from x to y is the same as distance from y to x so just pick a number D(distance) and do it that way. It is a more intuitive approach.

Answer 2

You don't need to know the distance between the two cities.
Average speed = Total distance/Total time
Let D be the distance between the two cities.
Total distance is 2D
Time going:
t = d/r
t = D/380
Time returning:
t = D/420
Total time = D/380 + D/420
Average speed = 2D/(D/380 + D/420)
= 2D/[D(1/380 + 1/420)]
= 2/(1/380 + 1/420)
= 2(380)(420)/(420 + 380)
= 319200/800
= 399miles/hr

Answer 3

D=RT
your missing some data

otherwise:

380+420/2 = 400

but your missing some data

Answer 4

i'm going to purpose to describe the main suitable i will: at the start, whenever you prefer to sparkling up for a variable (subsequently x), you're able to desire to place the variable on one side and the different numbers on the different. So first positioned the x on the left fringe of the equation. to do this, you would be conscious that x is unfavorable (-x). because of this, to stability the equation, you upload beneficial x to the two facets: 5 + x = 8 - x + x Now, you realize that -x + x equals 0, so which you would be able to now take that out of the equation: 5 + x = 8 Now you're able to desire to place the 5 on the main appropriate side so x could be on my own. you realize that 5 is a favorable variety (+5), with a view to stability the equation, you subtract 5 on the two facets: 5 - 5 + x = 8 - 5 5 - 5 equals 0, so which you would be able to now take that out of the equation: x = 8 - 5 you may now sparkling up x actually. x = 3 So this implies the in basic terms proper answer is x = 3 If we plug in 3 to the equation, we will se that it quite is genuine. 5 = 8 - 3 5 = 5 i'm hoping this helps =)