Homework Help
 

This is probably starting a new precedent for kids getting on the site to get their homework done, but I need help with my 9 year old's math. Just one question:
Wilbur and Orville fly 30 mi. in 1 hr. How many miles do they fly in one minute? I know the answer is half a mile, but could someone give me some logic or an example how to explain it so a 3d grader will understand how you got it?

It's a trick question. At 30 MPH, the plane wouldn't get off the runway.

30 miles in 1 hour
30 miles in 60 minutes
30 divided by 60 equals .50 or 1/2

That should be simple enough.

Distance = Rate x Time

eq. 1) D = R x T

Given: D = 30 miles and T = 1 hour

Place given in eq. 1) yielding

D = R x T
30 miles = R x 1 hour
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Solve for R the rate of speed of plane:

eq. 2) R = D / T = 30 miles/1 hour = 30 mi./hr.

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How far plane travel in ome minute:

D = R x T






eq. 3) D = (30 mi./hr.) x (1 minute)
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Notice that eq. 3) the minutes and hour is not the same units so you have to convert.

60 minutes = 1 hour

divide both sides by 60

60 minutes/60 = 1 hour / 60

eq. 4) 1 minute = 1/60 hour

Now place eq. 4). into eq. 3).

eq. 5) D = (30 miles/hour) x (1/60) hour = (30/60) miles = .5 miles

Note the hours cancel out yielding therefore

D = .5 miles


Note: The units always have to agree (match up) so for example when you divide it is not only numbers that your dividing but the units.

example: 5 minutes/1 hour = 5 (minute/hour)
this is right but you need to reduce to its least common factor by converting the hour to 60 minutes.

5 minutes/ 1 hour = 5 (minutes/hour) = (5 minutes) / (60 minutes)
=(1/12)
the minutes cancel out just given the 1/12
See how this makes more sense then 5 (minutes/Hour)

Will this work?

30mi = 1hr = 60min

30mi = 60min

Flip it around

How long would it take to go 1 mile - explain that you have to divide 30mi by 30 to get 1 mi, but you have to do the same to the minutes.

30mi/30 = 1 mi 60min/30 = 2 min

(my 3rd grader seemed to do well when the answer wasn't a fraction)

So, 1mi = 2 min

Than explain that to get to 1 minute you have to cut 2 minutes in half, but you have to do the same to same to the distance.

Put it all together and you get :wall: