Tutor MathsGuru: Ask me for your burning Maths questions!

[Dharma]

tianzhu:

Dharma:

I was thinking if 2 cuts of 36cm length spaced at 44cm are made perpendicular to the side of 47cm length leaving 1.5cm on either side. Then cut off the 44cm x 36cm x 24cm block from the original block and we are left with a U shaped block.
Really need Tianzhu’s help me on the illustration so that we can visualize better. This may gives a different total area.

Hi Dharma

Hope this helps.

Best wishes

http://farm5.static.flickr.com/4133/4950916508_849577cebf_b.jpg\">

Thanks Tianzhu. There is 1 more shape that will look like a rectangular hollow section with 1.5cm thickness on 2 sides and 1 thickness on the other 2 sides. Don't bother to draw it out. My guess is all 3 shapes will give different total areas.

[tianzhu]

Dharma:

Thanks Tianzhu. There is 1 more shape that will look like a rectangular hollow section with 1.5cm thickness on 2 sides and 1 thickness on the other 2 sides. Don't bother to draw it out. My guess is all 3 shapes will give different total areas.

Hi Dharma

Yes, how one cuts out the block (44*36*24) affects the surface area of the remaining block.

I am not sure if the question from the TS is reproduced exactly from the source or it has been summarised. How the question is worded has direct bearing on the answer.

If how the block is cut out is not expressly worded in the question, then one should go for the L shaped remainder which is easier to calculate the surface area.

Best wishes

[ganchiong]

Hi


To all the Maths Guru, appreciate if you could enlighten me on the following question.

The following question is taken from CHIJ St Nicholas 2009 P2 Q15:

A bullet train took 5 hrs to travel from P to H while an electric train took 4 hrs longer to travel from H to P. Both trains set off at the same time and moved towards each other. 2 hours later, they were 255 km apart. What was the speed of the electric train?

Thank you.

[tianzhu]

ganchiong:

The following question is taken from CHIJ St Nicholas 2009 P2 Q15:

A bullet train took 5 hrs to travel from P to H while an electric train took 4 hrs longer to travel from H to P. Both trains set off at the same time and moved towards each other. 2 hours later, they were 255 km apart. What was the speed of the electric train?

Hi
Hope this helps.

For bullet train, it took 5 hours to cover the journey.
So for 1 hour the bullet train will travel 1/5 of the journey

For electric train, it took 9 hours to cover the journey.
So for 1 hour the bullet train will travel 1/9 of the journey

Find the lowest common multiple of 5 and 9 which is 45.

Bullet train
9 units ----1 h
18 units ------2 h

Electric train
5 units ----1 h
10 units ------2 h

45 - 28 ------ 17

17 units ----- 255
1 unit ----- 15 km

Total distance ------ 45 units ----- 45 x 15 ------ 675 km

Speed of electric train -------675/9 -------75km/h

Best wishes

[ganchiong]

tianzhu:

ganchiong:

The following question is taken from CHIJ St Nicholas 2009 P2 Q15:

A bullet train took 5 hrs to travel from P to H while an electric train took 4 hrs longer to travel from H to P. Both trains set off at the same time and moved towards each other. 2 hours later, they were 255 km apart. What was the speed of the electric train?

Hi
Hope this helps.

For bullet train, it took 5 hours to cover the journey.
So for 1 hour the bullet train will travel 1/5 of the journey

For electric train, it took 9 hours to cover the journey.
So for 1 hour the bullet train will travel 1/9 of the journey

Find the lowest common multiple of 5 and 9 which is 45.

Bullet train
9 units ----1 h
18 units ------2 h

Electric train
5 units ----1 h
10 units ------2 h

45 - 28 ------ 17

17 units ----- 255
1 unit ----- 15 km

Total distance ------ 45 units ----- 45 x 15 ------ 675 km

Speed of electric train -------675/9 -------75km/h

Best wishes

Hi Tianzhu,

Thank you very much!

Cheers!

[acehkr3009]

Hi all,


I have a question here and my solution, but not too sure if method is appropriate for Pri level and if answer is correct. Need some feedback.

1/3 of the flowers in a park were Roses and the rest Hibiscus. 3/4 of the Roses were pink and the rest were red. 5/8 of the Hibiscus were red and the rest were pink. There were 156 pink flowers. How many flowers were there in the park?

1/3 Roses, 2/3 Hibiscus
3/4 of Roses are pink & 3/8 ( 1 - 5/8 ) of Hibiscus are pink

Fraction of pink Roses -> 1/3 x 3/4 = 1/4
Fraction of pink Hibiscus -> 2/3 x 3/8 = 1/4

Fraction of pink flowers -> 1/4 + 1/4 = 1/2

If 1/2 -> 156
2/2 -> 2 x 156 = 212

Total there is 212 flowers in the park

[acehkr3009]

Hi,


Here is another part whole question…

3 women donated some money to charity. The amount Alice donated was 1/4 the amount donated by Betty and Candy. The amount Candy donated was 1/2 the amount donated by Alice and Betty. Betty donated $250 more than Candy. How much was donated by all the 3 women?

I can used simultaneous equation to solve, but dont think my children can understand. Pls advise other ways for Pri level. Thanks.

Thanks

[acehkr3009]

Hi,


Here is another Part whole question…

A farm had pigs, goats and cows. 2/5 of the total number of animals in the farm were cows. 3/5 of the goats and twice as many cows were sold. 45 animals were sold. How many cows were left if there were 38 pigs?

Pls help on this question. Thanks.

[Dharma]

acehkr3009:

Hi all,


I have a question here and my solution, but not too sure if method is appropriate for Pri level and if answer is correct. Need some feedback.

1/3 of the flowers in a park were Roses and the rest Hibiscus. 3/4 of the Roses were pink and the rest were red. 5/8 of the Hibiscus were red and the rest were pink. There were 156 pink flowers. How many flowers were there in the park?

1/3 Roses, 2/3 Hibiscus
3/4 of Roses are pink & 3/8 ( 1 - 5/8 ) of Hibiscus are pink

Fraction of pink Roses -> 1/3 x 3/4 = 1/4
Fraction of pink Hibiscus -> 2/3 x 3/8 = 1/4

Fraction of pink flowers -> 1/4 + 1/4 = 1/2

If 1/2 -> 156
2/2 -> 2 x 156 = 212

Total there is 212 flowers in the park

Hi,

You workings are fine but the answer is 312

[blessedami]

acehkr3009:

Hi,


Here is another part whole question....

3 women donated some money to charity. The amount Alice donated was 1/4 the amount donated by Betty and Candy. The amount Candy donated was 1/2 the amount donated by Alice and Betty. Betty donated $250 more than Candy. How much was donated by all the 3 women?

I can used simultaneous equation to solve, but dont think my children can understand. Pls advise other ways for Pri level. Thanks.

Thanks

Hi,

This is how my DS worked it out:

A:B+C
1:4

C:A+B
1:2

Since the total is constant, we must find the LCM of ( 1+4 ) and ( 1+2 )

which is : 15

So, the ratio will become
A: B+C
3 :12

A+B
5: 10

So, Alice donated 3 units, Candy donated 5 units and therefore, Betty donated 7 units.

7u - 5u = 2u
2u---> $ 250
So, 15u----> $250 /2 x 15 = $ 1875