Q&A - PSLE Math

[Musicstar]

Oldschool,


Thank you for pointing out to me. I am really careless and did not read the question properly. The two words are really important. If don't have these two words \"the same\" which mean I need to change to the number of coin to the amount.

Oldschool:

Musicstar:

Hi,

Can someone enlighten me the below question with two types of method to solve the question but why different answer? Please advise the mistake. I suppose no matter which methods should also get the same answer. Thank you.

A box contained some twenty-coins and some fifty-cent coins in the ratio 3:4. When 26 fifty-cent coins were taken out and replaced by the same number of twenty-cent coins, the ratio became 4:1. Find the sum of money in the box in the box at first.


Working No 1
Since the number of coins did not change, we make the total the same

Before
T : F
3 : 4 (Total = 7u)
15 : 20 (Total = 35u)

After
T : F
4 : 1 (Total = 5u)
28 : 7 (Total = 35u)

13u = 26
1u = 2

15u of 20 cent = 15 x 2 x 0.2 = $6
20u of 50 cent = 20 x 2 x 0.5 = $20

Total = $26

Working No 2
Using units and parts
20cents : 50cents
3 units : 4 units
+65 -26 x 4
4 parts 1 part

3u +65 = 4p
16u -104 = 4p
3u + 65 = 16u - 104
16u - 3u = 65 + 104
13u = 169
u = 13
3u = 13 x 3 = 39
39 x $0.20 = $7.80
4u = 13 x 4 = 52
52 x $0.50 = $26
$7.80 + $26. = $33.80

Hi,

This is because in (b), instead of replaced with same number of coins, it is substituted with same amount of coins.

i.e. 65x20cents= 26x50cents in amount


But the question said \"same number\" though.

Regards

[rocklee]

Anyone can help?


There were a total of 20800 toys in Factory A and Factory B. After 3/4 of toys in Factory A and 3/5 in Factory B were sold, there were 1040 more toys in B than A. How many toys were there in each factory at first?

[CloudeeDaz]

rocklee:

Anyone can help?


There were a total of 20800 toys in Factory A and Factory B. After 3/4 of toys in Factory A and 3/5 in Factory B were sold, there were 1040 more toys in B than A. How many toys were there in each factory at first?

hihi
there is a solution http://www.kiasuparents.com/kiasu/forum/viewtopic.php?p=775568#p775568/

[CloudeeDaz]

and http://www.kiasuparents.com/kiasu/forum/viewtopic.php?p=23793#p23793%20/

[Musicstar]

Please help.Thank you


Q11) Sally , Yiling and Ali shared a bag of beads. Sally received 3/4 of the bag of beads and 3/4 of a bead. Yiling received 3/4 of the remaining bag of beads and 3/4 of a bead. Ali received the last bead in the bag. How many beads did Sally receive? (No bead was to be divided in any way)

Q17 ) Jane and Iris had 255 sweets altogether. Jane had 15 more sweets than Iris. Jane gave away 25% as many sweets as Iris. She was left with twice as many sweets as Iris.
(a) How many sweets did Iris give away?
(b) How many sweets did Jane have in the end?

[jieheng]

Musicstar:

Please help.Thank you


Q11) Sally , Yiling and Ali shared a bag of beads. Sally received 3/4 of the bag of beads and 3/4 of a bead. Yiling received 3/4 of the remaining bag of beads and 3/4 of a bead. Ali received the last bead in the bag. How many beads did Sally receive? (No bead was to be divided in any way)

............................................[---------------1u-------------]
[--------------------3u-------------------][3/4][------3p------][3/4][ 1]
...................................................................[---1p--]

S [--------------------3u-------------------][3/4]
Y [------3p------][3/4]
A [ 1]

1p --> 1 + 3/4 = 7/4
4p --> 7

1u --> 3/4 + 4p = 3/4 + 7 = 31/4

Sally --> 3u + 3/4 = 3*(31/4) + 3/4 = 96/4 = 24

[jieheng]

Musicstar:

Please help.Thank you


Q17 ) Jane and Iris had 255 sweets altogether. Jane had 15 more sweets than Iris. Jane gave away 25% as many sweets as Iris. She was left with twice as many sweets as Iris.
(a) How many sweets did Iris give away?
(b) How many sweets did Jane have in the end?

J [-----------------][15]
I. [-----------------]

J [][---------------][15]
I. [][][][][---------]

J [][----][15][----][15]
I. [][][][][15][----]

J [][][][][15][][][][15] --> 7u + 30
I. [][][][][15][][][] --> 7u + 15

7u + 30 + 7u + 15 --> 255
14u --> 210
1u --> 15

a)

No of sweets that Iris gave away = 4u = 4*15 = 60

b)

No of sweets that Jane had in the end = 6u + 30 = 6*15 + 30 = 120

[Musicstar]

Hi,


Can someonehelp to explain to me my doubt. Why u= 2u -1040 , 4u = 4 (2u-1040 ) & 5u +8u -4160. Thank you very much.

small:

ks2me:

http://i724.photobucket.com/albums/ww246/ks2me/P6MathRiceSacks-1.jpg\">

Thanks again ks2me, you are great...

No wonder I not able to get the answer due to my wrong calculation; 1920 x 5 = 9100.

[Oldschool]

Musicstar:

Hi,


Can someonehelp to explain to me my doubt. Why u= 2u -1040 , 4u = 4 (2u-1040 ) & 5u +8u -4160. Thank you very much.

small:

[quote=\"ks2me\"]http://i724.photobucket.com/albums/ww246/ks2me/P6MathRiceSacks-1.jpg\">

Thanks again ks2me, you are great...

No wonder I not able to get the answer due to my wrong calculation; 1920 x 5 = 9100.

[/quote]
Hi,

There is a difference in the 2 \"u\".

One is small \"u\" and the other is big \"U\".

So, for clarity you can replace one of it with P and it will end up as UP method.

http://www.flickr.com/photos/94858125@N03/8662494378/in/photostream/

Hope this help.

Regards

[MathIzzzFun]

rocklee:

Anyone can help?


There were a total of 20800 toys in Factory A and Factory B. After 3/4 of toys in Factory A and 3/5 in Factory B were sold, there were 1040 more toys in B than A. How many toys were there in each factory at first?

Toys unsold:
Factory A --> 2 units -- 1/4 of total
total in Factory A at first --> 8 units

Factory B --> 2 units + 1040 = 2 x ( 1 unit +520) --- 2/5 of total
total in Factory B at first = 5 x ( 1 unit + 520 ) = 5 units + 2600

At first, total number of toys:
13 units + 2600 = 20800
1 unit --> 1400

At first,
Factory A --> 11 200 toys
Factory B --> 9 600 toys

cheers.