Q&A - PSLE Math

[stary]

Hi Tianzhu,


Impressed by yr precise solutions with models. I have a question, see if u could help.

Dennis had 80 more stickers than Karen. Dennis gave 25% of his stickers to Karen. Karen in return gave 60% of her stickers to Dennis. In the end, Dennis had 92 stickers more than Karen. How many stickers did Dennis have at first?

Stary

[stary]

Hi all,

I have a question in doubts, need some assistance. Tks u:)

20% of John’s savings is $120 more than 30% of Brian’s savings. After John spent 5/6 of his savings and Brian spent 1/2 of his savings. John has $20 more than Brian. Find John’s savings at first.

[tianzhu]

stary:

Hi Tianzhu,


Impressed by yr precise solutions with models. I have a question, see if u could help.

Dennis had 80 more stickers than Karen. Dennis gave 25% of his stickers to Karen. Karen in return gave 60% of her stickers to Dennis. In the end, Dennis had 92 stickers more than Karen. How many stickers did Dennis have at first?

Stary

Hi Stary

Please follow the following steps if you choose to use MD.

At First
Dennis -------- 4 units + 80
Karen ------- 4 units

After Dennis gave 25% of his stickers to Karen.
Dennis ------ 3 units + 60
Karen ----- 4 units + 1 unit + 20 ----- 5 units + 20

After Karen in return gave 60% of her stickers to Dennis.
Dennis ------- 3 units + 60 + 3 units + 12 ------- 6 units + 72
Karen ------- 2 units + 8

In the end, Dennis had 92 stickers more than Karen.
6 units + 72 ------- 2 units + 8 +92
4 units ------- 28
1 unit ------- 7

At First
Dennis ------ 4 units + 80 ------ (4*7) + 80 ------108

Best wishes

[tianzhu]

stary:

Hi Tianzhu,


Impressed by yr precise solutions with models. I have a question, see if u could help.

Dennis had 80 more stickers than Karen. Dennis gave 25% of his stickers to Karen. Karen in return gave 60% of her stickers to Dennis. In the end, Dennis had 92 stickers more than Karen. How many stickers did Dennis have at first?

Stary

Hi Stary

If you wish to use the Units Method, please refer to one of my earlier posts for a similar type of question@Wed Dec 29, 2010 8:13 am by following this link.

http://www.kiasuparents.com/kiasu/forum/viewtopic.php?t=280&postdays=0&postorder=asc&start=2230

Best wishes

[small]

Hi Stary,


Please find the solution.

http://farm6.static.flickr.com/5218/5430439977_6b9192fa7c_z.jpg\">

[Vanilla Cake]

7/9 of a square is coloured purple. Delia wants to cut 1/2 of this part into smaller pieces such that each piece is 3/25 of the whole square. What is the maximum number of pieces that she can cut?


Answer given is 2 pieces. Is this correct?
Thanks for your reply.

[stary]

Thank you to tianzhu and small for yr great solutions. So happy that my doubts are clear.

[small]

Hi Stary,


You are welcome...Tianzhu is my 'shi fu'..

:celebrate:

[small]

Vanilla Cake:

7/9 of a square is coloured purple. Delia wants to cut 1/2 of this part into smaller pieces such that each piece is 3/25 of the whole square. What is the maximum number of pieces that she can cut?


Answer given is 2 pieces. Is this correct?
Thanks for your reply.

If my understanding is correct, it very depends on how they coloured the square. By calculation, it should not more than 3 pcs..

7 / 9 x 1/2 = 7/18

7/18 x 25/3 = 3R13

[Dharma]

stary:

Hi Tianzhu,


Impressed by yr precise solutions with models. I have a question, see if u could help.

Dennis had 80 more stickers than Karen. Dennis gave 25% of his stickers to Karen. Karen in return gave 60% of her stickers to Dennis. In the end, Dennis had 92 stickers more than Karen. How many stickers did Dennis have at first?

Stary

Hi Stary,

This is another of looking at the problem ...

Number of stickers that Dennis and Karen had in total did NOT change because the exchange of stickers were done between them only.

At first
Dennis : 100u + 80
Karen : 100u
Total : 200u + 80

At last
Total : 200u + 80
Karen : (200u + 80 – 92)/2 = 100u - 6
Dennis : 100u – 6 + 92 = 100u + 86

No. of stickers Karen had after receiving 25% of Dennis’s stickers is the same as the no. of stickers she had before returning 60% of her stickers to Dennis.
100u + ¼ (100u + 80) = 5/2 (100u – 6)
125u + 20 = 250u - 15
125u = 35
100u = 28
No. of stickers Dennis had at first = 100u + 80 = 28 + 80 = 108