Q&A - PSLE Math

[stary]

MathIzzzFun:

stary:

[quote=\"stary\"]Hi all,


Have a question...

Ali and Baba ran in a race. When Baba had completed the race, Ali had only run 5/8 of the distance. Baba's speed was 75 m/min faster than Ali's speed. Both of them did not change their speeds throughout the race.
What was Ali's speed in m/min?

Appreciate your help... :?

Someone help me!

Hi

Ratio of Baba’s speed to Ali’s speed
=Sbaba: Sali
= 8u: 5u

Difference in speed = 3u = 75m/min
1u = 25m/min

Ali’s speed = 5u = 5 x 25m/min = 125m/min

cheers.[/quote]Thanks MathIzzzFun!

[stary]

wkong:

stary:

[quote=\"wkong\"]Need help for the following question:-


Qn2

http://i51.tinypic.com/2q8d9bb.jpg\">

Unshaded/2 -> (1 - 1/4) / 2 = 3/8
1 rectangle -> 3/8 + 1/4 = 5/8
5/8 of figure ->5x 12 = 60 cm2
Figure -> 8/5 x 60 = 96 cm2

Thanks Stary.[/quote]Glad to help...

[tianzhu]

small:

Please help and many thanks in advance.


Question from a school paper:
Ben bought some bottles of glue for $20. He wanted to sell each bottle of glue for 40 cebts but only managed to sell 12 bottles. He then decided to lower the price and sold the remaining bottles for a total of $22.91.

(a) What was the lower price he sold each bottle for?
(b) How many bottles were sold at the lower price?

:?

Hi small

Good Morning.

What are the answers?

It looks like there is some missing information.

Best wishes

[pixiedust]

Would greatly appreciate some help with the following question. I need solution withOUT using Unit Transfer please.

Thank you :

Larry had some red and blue marbles in the ratio 2:5. After he bought another 30 red marbles and 15 blue marbles, the ratio became 4:7. How many marbles did Larry have at first ? Answer : 175 marbles

[lizawa]

pixiedust:

Would greatly appreciate some help with the following question. I need solution withOUT using Unit Transfer please.

Thank you :

Larry had some red and blue marbles in the ratio 2:5. After he bought another 30 red marbles and 15 blue marbles, the ratio became 4:7. How many marbles did Larry have at first ? Answer : 175 marbles

Red : Blue
= 2 : 5
(+30 red and + 15 blue)
= 2u + 30 : 5u + 15
= 4 :7

7(2u +30) = 4 (5u+15)
14u +210 = 20u +60
6u = 150
1u = 25
AT first -> 7u = 7 x 25 = 175.

[Brenda10]

pixiedust:

Would greatly appreciate some help with the following question. I need solution withOUT using Unit Transfer please.

Thank you :

Larry had some red and blue marbles in the ratio 2:5. After he bought another 30 red marbles and 15 blue marbles, the ratio became 4:7. How many marbles did Larry have at first ? Answer : 175 marbles

Hi pixiedust

Sorry, deleted as wrong post.

[pixiedust]

lizawa, thanks...but how to explain to P5/6 this step :

\"= 2u + 30 : 5u + 15
= 4 :7
7(2u +30) = 4 (5u+15)..\"

Brenda, no problem. If your dd has any other way to solve, do update too. thanks in advance.

[wkong]

MathIzzzFun:

Hi

http://i52.tinypic.com/161aijn.jpg\">

cheers.

Thanks again MathIzzzFun

[tianzhu]

pixiedust:

Would greatly appreciate some help with the following question. I need solution withOUT using Unit Transfer please.

Thank you :

Larry had some red and blue marbles in the ratio 2:5. After he bought another 30 red marbles and 15 blue marbles, the ratio became 4:7. How many marbles did Larry have at first ? Answer : 175 marbles

Hi pixiedust

In this question, different numbers of marbles are added to the initial quantities; hence the total number of marbles (red and blue) in the end is not the same as in the beginning.

You may use MD or Units and Parts (UP) to solve it.

Due to time constraints, I shall skip drawing the MD but would describe the steps as in MD.

Draw 2 boxes to show red marbles and 5 similar boxes to show blue marbles. Further divide these boxes into 4 boxes and 10 boxes using equivalent ratios.

Draw another box to show 30 red marbles and add to the 4 boxes(red).At the same time, add another box showing 15 marbles to the 10 boxes(blue).
So we have 4 red boxes plus 30 red marbles and 10 blue boxes plus 15 blue marbles.

In the end we have 1 red box plus 7.5(30/4) to show 1 part
We have 4 red boxes plus 4 boxes of 7.5 and 7 blue boxes plus 7 boxes of 7.5 in the end. This shows the final ratio of 4:7.

Comparing,we have 10 units + 15 equal to 7 units + 7*(7.5), giving 1 unit equals to 12.5.

Larry has 14 units or (14*12.5) which is 175.

If you have a copy of this book, Challenging Maths Made Easy, you may also refer to the solution using UP.It’s quite similar to lizawa’s solution. Instead of cross multiplication and expansion of brackets, it uses equalisation of parts as a comparison.You may refer to a solution of a similar type of question using UP in one of the earlier posts.

http://farm6.static.flickr.com/5019/5444329416_183f66d5eb_z.jpg\">

Best wishes

[pixiedust]

tianzhu, thank you very much !

I am struggling at the last step of the MD, I will draw it out again to get your point.

I do have the book and explored the UP method. However, I cannot find an effective way to explain (1) why is it necessary to make the parts the same - in your diagram ie. 16 parts or 28parts in my problem sum (2) for questions with -ve quantity, the part must be moved to the other identity. I am afraid if I cannot explain the rational behind these 2 steps, ds will just memorise the steps and unable to apply UP method effective. Would appreciate any suggestions.