Maths Help

ladyy · Post by **ladyy** » Thu Aug 23, 2007 10:28 am

Please can someone explain how to solve the questions below?

Frank takes 2 hours minutes to do a journey at an average speed of 40 mph. How far does he go.

Janet does the same journey in 2 hours. What is her average speed?

Cheers

Catherine · Post by **Catherine** » Thu Aug 23, 2007 11:07 am

Hi, ladyy, you have forgotten to give the number of minutes that Frank takes. I'll say 30 minutes.

If frank goes at 40mph, he goes at 40/60 miles (=2/3 mile) per minute.

So in 1 minute, he does 2/3 mile.
In 2 hours 30 minutes (=150 mnns) he does 2/3 mile * 150 = 300/3 = 100miles

Janet does 100 miles in 2 hours , so 50 miles in 1 hr. Her speed is 50mph.

Hope this helps

Catherine

ladyy · Post by **ladyy** » Thu Aug 23, 2007 11:34 am

I typed the question wrongly, it should be

Frank takes 2 hours 30 minutes to do a journey at an average speed of 40 mph. How far does he go.

Janet does the same journey in 2 hours. What is her average speed?

I now know how to explain it to my son.

Thanks a once again.

MelX · Post by **MelX** » Thu Aug 30, 2007 12:24 pm

Hi there

I reckon this

If he does 40 miles per hour and he has done 2 hours 30 minutes then

2 hours = 80 miles
30 minutes = 20 miles
Total 100 miles

If Janet does the same distance in 2 hours then

100 miles devided by 2 = 50 miles per hour thus her avergae 50mph

Guest · Post by **Guest** » Fri Aug 31, 2007 4:18 pm

Brilliant, simple expanation. Thanks MelX

KenR · Post by **KenR** » Fri Aug 31, 2007 8:53 pm

I think the important point here is to make they learn the 3 different SDT equations, and also remember to convert time into the correct units.

In my children's junior school (a few years ago now) they did study skills lesson and used a SDT pyramid method to help the children remember (and work out) the 3 equations: S=D/T etc.

In theory it's not essential for 11+ but my children found this invaluable. If they are doing any Independent 11+ exams as well then this is certainly essential.

ladyy · Post by **ladyy** » Mon Sep 03, 2007 4:03 pm

Please can you explain what the SDT Pyramid method is.

Many Thanks

KenR · Post by **KenR** » Mon Sep 03, 2007 4:23 pm

I'm not totally sure of the method myself, but it was something my daughter was taught in school to remember the 3 equestions:-

Speed = Distance/Time
Speed x Time = Distance
Time = Distance/Speed

I seem to recall they got the children to write SDT in a pyramid with D at the top, S on the left and T on the Right. They then drew perpendicular lines from the centre of each side to a point in the middle of pyramid.

No sure why this did this, I've always remembers S=D/T and then just simply rearranged!

Ken

Guest · Post by **Guest** » Mon Sep 03, 2007 5:46 pm

Kenr, as you say you have D on top, line and S X T on bottom. The idea is that you cover the one you want and this gives you how to calculate it. Thus, if you cover the D, you are left with S x T. If you cover the S, you see D/T (i.e. D divided by T) etc.
Unfortunately the children who don't get the whole concept of speed, time and distance tend to be the same children who can't remember which number is where in the triangle.
They do these same triangles further up the school in the sciences as an aide to memory.