Q&A - PSLE Math

[small]

Change to use firefox and it solved the problem.

[camomile]

Hi…can anyone help me with the following problem?


Uncle Sam paid $5250 for a plasma television. He paid the exact amount in $1oo and $50. He gave the cashier 90 notes in all. How many of them were $50 notes?

Ans: 75

I managed to solve it with the following ‘expression’:

100u + (90 x 50) - 50u = 5250
50u + 4500 = 5250
u = 750/50 = 15

therefore, no. of $50 = 90 - 15 = 75

Am trying to help coach my nephew as the parents can’t afford tuition (Dad was retrenched last year). But I don’t know how to explain to my nephew using the modeling method.

[Ruru]

Hi,my method is not the \"model\" method. It's based on assuming.


Let's say Uncle Sam gave the cashier 90 $100 notes. Then he would have given (90x$100) - $5250 = $3750 extra. If he were to exchange some of the $100 notes with $50 notes,how many he would need to exchange would be the answer to how many $50 notes there are.

For example,if he takes back $100 from the cashier and gives the cashier $50,the difference is $50. He has to divide $3750(the extra money) by the difference of $50 in order to find out how many $50 notes he needs to exchange.

Hence,$3750 divide by $50 = 75.

He has to take back 75 $100 notes and also give the cashier back 75 $50 notes. Since in the beginning we have already assumed that all the notes he gave were $100 notes,the exchanged 75 $50 notes is the answer. (He only exchange 75 notes,remember? So the rest were untouched.)

Hope u understand.

[camomile]

Hi Ruru....thanks for your help.


I managed to solve this problem using the assuming method too after having my dinner....Ha ha....can't work on on empty stomach.

If all notes are $50, 90 x $50 =$4500

remaining money (which are the halves of the $100) will be
5250 - 4500 = 750

750/50 = 15 (number of $100)

90 - 15 = 75 (ans)

Based it on one of the questions ( think its the legs of cows and chickens or something) in this thread. I'm so glad there's a forum like this for 'challenged' aunty like me

[lizawa]

small:

lizawa:

[quote=\"tianzhu\"]Maths Questions from http://www.channelnewsasia.com/discussion/forum.htm


3. A group of people met at a party. Each person shook hands with everyone else. Mr Li shook hands with 3 times as many men as women. Mrs Li shook hands with 4 times as many men as women. How many men and how many women were there at the party?

Answer : no. of men = 16; no. of women = 5

See working :

http://www.postimage.org/image.php?v=gx2w0utS

Hi lizawa,

I was not able to see the picture clearly, please can you send it to me or repost? thanks in advance.

Anyway I have to say thanks to all, great forum...help me a lots. :)[/quote]Hi small,

I just PM you. Give me your email address and I will email the solution to you.

lizawa

[tianzhu]

Thank you for your help.


http://farm4.static.flickr.com/3340/3247272886_c4b735f5ec_o.jpg\">

[ChiefKiasu]

tianzhu:

Thank you for your help.


http://farm4.static.flickr.com/3340/3247272886_c4b735f5ec_o.jpg\">

The sequence is in 3s:
1 2 3, 4 5 6, 7 8 9, ... (POSITION)
2 3 4, 3 4 5, 4 5 6, ...

Number of blocks of 3 between 1 and 100 inclusive = (100 - 1) /3 = 33
The number at the 100th position should be = 33 + 2 = 35

[lizawa]

Hi small,


here is the solution. thanks to tianzhu for pointing out the best way to insert this image.
http://farm4.static.flickr.com/3313/3249159538_c8d4e72e9e_b.jpg\">

[tianzhu]

Thank you for your help.



http://farm4.static.flickr.com/3440/3249871151_68fb7b9636_o.jpg\">

http://farm4.static.flickr.com/3400/3249871171_17aac5eb58_o.jpg\">

[ksmama]

looking at column 1 and 2

pattern 1 -> 4 toothpicks ( 1 x (4+0))
patt 2 -> 10 tp ( 2 x (4+(2-1))
patt 3 -> 18tp ( 3 x (4+(3-1))

therefore patt 10 needs 10 x (4+(10-1)) = 10x13 = 130 tp

patt 438 needs 438 x ( 4 + (438-1)) = 438 x 441 = 193158 tp

Now look at column 2 and 3

patt 1 -> 4tp->1diamond (4/2 - 1)
patt 2 -> 10tp->3diam (10/2 -2)
patt 3 -> 18tp->6diam (18/2 -3)

therefore patt 18 needs 18x(4+(18-1))=378tp which makes (378/2 - 18)=171 diamonds

and patt 500 needs 500x(4+(500-1))=251500 tp which makes (251500/2 - 500) =125250 diamonds