Q&A - PSLE Math

[tianzhu]

SAHMwith2boys:

Hi, need help in this Maths question:


Every desk has 4 stools surrounding it. How many desks and stools are there if there are x more stools than desks?

Hi

Hope this helps.

Best wishes.

http://farm9.staticflickr.com/8083/8343943343_1d944d95e8_z.jpg\">

[CoffeeCat]

SAHMwith2boys:

CoffeeCat:

[quote=\"SAHMwith2boys\"]Hi, need help in this Maths question:


Every desk has 4 stools surrounding it. How many desks and stools are there if there are x more stools than desks?

In the first place, dun understand the question.... :scratchhead:

I think it means...
For every desk that exists in this fictional mathematical world, there is 4 stools surrounding it.
So there are 4 times as many stools as desks.


Just in case ....
so if number of desks is 1 unit, number of stools is 4 units.
Difference, 3 units = x
Total number of desks & stools = 5x/3

Answer provided was:

No. of desks : No. of stools = 1 : 4 = x : 4x
There are x desks.
There are 4x stools.

Anyone can help to decipher why the solution is this and what does the question wants?? :?[/quote]hmm I misread the question as \"total number of desks and stools\".
Anyway maybe there was a typo in the question. They meant to say there are x desks and not x more stools than desks.

[Dad8282]

Hi,


Need help with the following questions:

1. I have some red and blue ribbons in a bottle.
If I add in 20 red ribbons, 60% of my ribbons are blue.
If I add in another 60 blue ribbons, 75% of my ribbons are blue.
How many ribbons have I in the bottle?

2. Rectangle A overlaps with Rectangle B. Rectangle A is twice the size of Rectangle B.
If 1/3 of Rectangle B overlaps with Rectangle A, what fraction of Rectangle A
overlaps with Rectangle B?

Thanks.

[tianzhu]

Hi


Q1 has been discussed in our earlier posts.

You may wish to refer to them.

http://www.kiasuparents.com/kiasu/forum/viewtopic.php&f=69&t=280&p=712514

Best wishes

[tianzhu]

Dad8282:

2. Rectangle A overlaps with Rectangle B. Rectangle A is twice the size of Rectangle B.
If 1/3 of Rectangle B overlaps with Rectangle A, what fraction of Rectangle A
overlaps with Rectangle B?

Thanks.

Hi

A neat way is to use MD or draw two boxes of different sizes and labeling them with units.

Draw 6 boxes to show the size of rectangle A. Use 5 boxes to show its unshaded portion and 1 box to show the shaded portion.

Draw 3 boxes to show the size of rectangle B. Use 2 boxes to show unshaded area, the shaded portion is the same as rectangle A.

Hence, fraction of A overlapping B ------ 1/6

Best wishes

[Dad8282]

Good Morning Tianzhu,


Thank you for your explanation and pointing me to the correct page for the answer!

Have a nice day!

[mathnoobs]

Hi Mathizzfun

I recently came across this problem and found that you have the answer. http://www.kiasuparents.com/kiasu/forum/viewtopic.php?f=69&t=280&start=7640


Abel and Ben can build a model aircraft together in 4 days. Ben and Calvin can do the same job together in 1 1/2 times as many days. Abel and Calvin can complete the same job together in twice the number of days Ben and Calvin can do together. If the three boys decide to work together, how long will they take to complete their job?
(Answer: 4 Days)

However, I don't quite understand this line:
Work needed to complete job --> 12 units

how do you get the 12 units ? thanks in advance.

[dazzlego]

mathnoobs:

Hi Mathizzfun

I recently came across this problem and found that you have the answer. http://www.kiasuparents.com/kiasu/forum/viewtopic.php?f=69&t=280&start=7640


Abel and Ben can build a model aircraft together in 4 days. Ben and Calvin can do the same job together in 1 1/2 times as many days. Abel and Calvin can complete the same job together in twice the number of days Ben and Calvin can do together. If the three boys decide to work together, how long will they take to complete their job?
(Answer: 4 Days)

However, I don't quite understand this line:
Work needed to complete job --> 12 units

how do you get the 12 units ? thanks in advance.

I guess he assume that the number of work done is the LCM of 4, 6 and 12. Since A+B = 4 days, B+C = 6 days, A+C = 12 days

[charsen]

dazzlego:

mathnoobs:

Hi Mathizzfun

I recently came across this problem and found that you have the answer. http://www.kiasuparents.com/kiasu/forum/viewtopic.php?f=69&t=280&start=7640


Abel and Ben can build a model aircraft together in 4 days. Ben and Calvin can do the same job together in 1 1/2 times as many days. Abel and Calvin can complete the same job together in twice the number of days Ben and Calvin can do together. If the three boys decide to work together, how long will they take to complete their job?
(Answer: 4 Days)

However, I don't quite understand this line:
Work needed to complete job --> 12 units

how do you get the 12 units ? thanks in advance.

I guess he assume that the number of work done is the LCM of 4, 6 and 12. Since A+B = 4 days, B+C = 6 days, A+C = 12 days

Hi
Dazzle go,your explanation is correct.

[MathIzzzFun]

mathnoobs:

Hi Mathizzfun

I recently came across this problem and found that you have the answer. http://www.kiasuparents.com/kiasu/forum/viewtopic.php?f=69&t=280&start=7640


Abel and Ben can build a model aircraft together in 4 days. Ben and Calvin can do the same job together in 1 1/2 times as many days. Abel and Calvin can complete the same job together in twice the number of days Ben and Calvin can do together. If the three boys decide to work together, how long will they take to complete their job?
(Answer: 4 Days)

However, I don't quite understand this line:
Work needed to complete job --> 12 units

how do you get the 12 units ? thanks in advance.

We need to find the work rate in units/day. So, in order to \"avoid\" working in fractions, set the amount of work done (in assembling the aircraft) to be the LCM of 4,6 & 12

cheers.