Tutor MathsGuru: Ask me for your burning Maths questions!

[Brenda10]

Emelyn:

Brenda10:

[quote=\"Emelyn\"]
Sorry... Brenda10...I actually thought I understood... but then I realised that I didn't. :oops:

Can you explain how you get

24U = 160
20U = 200

?

Q1.
D:A
3:4
+20 +40
5:8
24U =160
20U =200

Use cross-multiplication (end units : 5 and 8 respectively)
(3u + 20)*8 = 24u 160
(4u + 40)*5 = 20u 200

Ok. Understand now how you get 24U 160....
But...paiseh hor...... why need to cross multiply lei ?? What are we trying to achieve ?
:oops: :oops: :oops:[/quote]This question is classifed under : External Change

To solve this type of problem is to make the end the same. As such we can find the qty represent in the units.

Sorry not good in explanation :oops: but when dual with this type of External Change question we will then use the above cross multiply method.

[CJM]

small:

CJM:

Dave had 59 toy cars and toy soldiers. After giving away 1/3 of his toy cars and 4 of his toy soldiers, he had an equal number of toy cars and toy soldiers. How many toy soldiers did he have at first ?

Hi CJM,

Here is the solution, hope it helps.

http://s4.postimage.org/bcLA9-0c78d7a2.png\">

Hi Small,

I cant see the solution .

Can u pls attach again ?

Thanks

[hamsterss]

Can anyone help me solve the question below?


A car and a coach travelled from town A to town B.The coach left town A at 0648 and it took 5hours to reach town B.The car started 30minutes later than the coach and it took 4 hours to reach town B.At what time did the car catch up with the coach?

Thanks

[Vanilla Cake]

hamsterss:

A car and a coach travelled from town A to town B.The coach left town A at 0648 and it took 5hours to reach town B.The car started 30minutes later than the coach and it took 4 hours to reach town B.At what time did the car catch up with the coach?

Pls refer to http://www.kiasuparents.com/kiasu/forum/viewtopic.php?p=205278 posted by myself, Uncle Dharma, http://prischoolmaths.blogspot.com/2009/09/combined-hokkien-speed-question.html and plus http://www.postimage.org/image.php?v=aVtOdzJ.

[Vanilla Cake]

CJM:

Dave had 59 toy cars and toy soldiers. After giving away 1/3 of his toy cars and 4 of his toy soldiers, he had an equal number of toy cars and toy soldiers. How many toy soldiers did he have at first ?

TC: Toy cars
TS: Toy soldiers

TC: [][][]
TS: [][][4]

[][][]+[][][4]=59
5[]=59-4=55
[]=11

Toy soldiers (at first) = [][]+4 = 2x11+4=26

Check
At first
Toy cars: 3x11=33
Toy soldiers: 2x11+4=26

Change
Gave away 1/3 of his toy cars and 4 of his toy soldiers.
1/3 of toy cars = 1/3x33=11

In the end
Toy cars: 33-11=22
Toy soldiers: 26-4=22

22=22
In the end, Dave had an equal number of toy cars and toy soldiers.

[last minute mama]

Dear Maths guru,


Please help to solve this question.
Raju and Ali started drving towards each other at the same time from Towns A and B respectively. They first met each other 10 km away from Town A. When Raju and Ali reached Towns B and A respectively, they turned back immediately and drove towards each other. If Raju and Ali met again 7 km away from Town B, what is the distance between Town A and B?

[Dharma]

last minute mama:

Dear Maths guru,


Please help to solve this question.
Raju and Ali started drving towards each other at the same time from Towns A and B respectively. They first met each other 10 km away from Town A. When Raju and Ali reached Towns B and A respectively, they turned back immediately and drove towards each other. If Raju and Ali met again 7 km away from Town B, what is the distance between Town A and B?

Raju meets Ali after travelling 10km from Town A. Raju has to travel another 20km towards Town B and turn back before he meets Ali again who has to travel to Town A and turns back.

Let the distance between the point they meet the 1st time and 2nd time be X

Distance travelled by Raju from the time he meets Ali for the 1st and the time he meets Ali the 2nd time
=Xkm + 7km + 7km = 20km
X = 6km

Distance between Town A and Town B = 10km + 6km + 7km = 23km

[last minute mama]

Dear Dharma,


Thanks for your prompt response. I could not understand why the equation is x+7 + 7 = 20?

After they met at P,
x+7+7 is distance travelled by Raju
x + 10 + 10 is distance travelled by Ali
When they meet again at Q (7 km from Town B)?

Not sure how this works. Please explain.

[iFruit]

last minute mama:

Dear Dharma,


Thanks for your prompt response. I could not understand why the equation is x+7 + 7 = 20?

After they met at P,
x+7+7 is distance travelled by Raju
x + 10 + 10 is distance travelled by Ali
When they meet again at Q (7 km from Town B)?

Not sure how this works. Please explain.

Lets say distance between A & B = D
Total dustance traveled by Raju & Ali when they met first time = D
Total distance traveled by Raju & Ali when they met second time = 3D
Total distance traveled by Raju when they met first time = 10
so, the total distance traveled by Raju when they met second time = 3x10 =30

So the distance from P, that raju traveled = 30 - 10 =20

[Dharma]

last minute mama:

Dear Dharma,


Thanks for your prompt response. I could not understand why the equation is x+7 + 7 = 20?

After they met at P,
x+7+7 is distance travelled by Raju
x + 10 + 10 is distance travelled by Ali
When they meet again at Q (7 km from Town B)?

Not sure how this works. Please explain.

This is a meeting problem of 2 persons leaving at the same time and moving towards each other. When they meet, the time taken by Raju and Ali is the same.
When they meet for the first time at P, the total distance travelled by Raju and Ali is actually the distance between the 2 towns .

When they meet for the 2nd time at Q, both take equal time to travel from P to Q (point where they meet again)
Raju travels X km (from P to Q) + 7 km ( Q to Town B ) + 7km ( Town B to Q) while Ali travels 10km ( P to Town A) + 10km ( Town A to P ) + X km ( P to Q)

The ratio of the distances travelled by Raju and Ali will be the every time they newer before the time they take is the same to meet.
However, when the meet at Q, the total distance covered by Raju and Ali will be 2 times the distance of Town A and Town B.
Therefore total distance trvelled by Raju from P to Q ( point where he met Ali) will double to 20km

so, X + 7 + 7 = 20
X = 6

distance travelled by Ali when he met Raju at P for the 1st time is 13km ( 7 + 6) km.

You will realize that of u work out Ali will travel another 13km x 2 = 26km before he meets Raju at Q for the 2nd time.

20km + 26km = 46km ( twice the distance between Town A and B)

This qn is quite similar to 2 persons on opposite end of a circular track and running towards each. When they meet for the 1st time they would have run half the circumference of the track and when they meet for the 2nd time they would have covered the circumference of the track in total.