What is 513 rounded to the nearest ten ?

p = plane's speed in calm air

w = wind's speed

p + w = speed across the ground of the plane flying with the wind

p - w = speed across the ground of the plane flying against the wind

d = rt is the standard distance equation, where d=distance, r=rate, t=time

d = 800 miles is given

800 = 4(p+w) :: given that it takes 4 hrs with the wind to travel 800 miles

800 = 5(p-w) :: given that it takes 5 hrs against the wind to travel 800 miles

so we have

4(p+w) = 800

5(p-w) = 800

4p + 4w = 800

5p - 5w = 800

multiply the first equation by 5 and the second by 4

20p + 20w = 4000

20p - 20w = 3200

add them

40p = 7200

p = 180

substituting for p = 180, we can find w

4p + 4w = 800

divide by 4

p + w = 200

180 + w = 200

So,

w = 20

checking our work.

4(180+20) = 800??

4(200) = 800

Yes

5(180-20) = 800??

5(160) = 800

Yes.

The Plane flies at 180 mph in calm air.

The Wind is blowing at 20 mph.

Hope This Helps! Merry Xmas:)