Q&A - PSLE Math

[Oldschool]

Musicstar:

Hi,


Can someone help to explain the following questions? Although my girl is already P6 but I have been doing this type of questions but still do not understand when to \"+\" and \"-\". How do I look at the question to understand? Can someone enlighten me to better understanding? My girl has this question wrong. I think she also still not sure how to do it. Sorry, it may be an easy question for others. Thank you for helping to explain.

Questions: Vicky and her sister have a sum of money . If Vicky gives $120 to her sister, she will have 3 times as much money as her sister. If Vicky gives an additional $40 to her sister, she will have $240 more than her sister . How much money does her sister have?

Answer : 2u = 40 +40+40 = $320
1 u = 160
160 - 120 =40
Her sister has $40.

Hi,

The person who gives will have that sum deducted from his/her share.

Likewise, the person who receives will have that sum added to his/her share.

For a start, it is good to draw table/model and fill it in with the information/clue given.

Perhaps then, it would easier to follow/see and determine what other information is needed to help solve the problem.

Regards

http://www.flickr.com/photos/94858125@N03/8651246076/sizes/c/in/photostream/

[tianzhu]

PapayaDad:

Hi tianzhu,


I learn from your blog too. Thanks a lot.

Hi PapayaDad

So paiseh , actually, the blog was not set up by me because I don’t know how to blog.

You know lah, old man already, only know of “blocks’ in life, not “blogs”

It was Chief who helped to transfer the post from the P5 thread to the blog.

Best wishes

[Easy-going]

Hi

Please help me with this question. Thank you very much in advance.
Question 14 (Rosyth CA 1 2012 Paper Two)
Jack, Meili and Raj shared some 50-cent coins.
They each had an average of 28 coins.
The total amount of money that Jack and Meili had was $7 more than the total amount of Jack and Raj had.
If Raj’s amount was 4 times of Jack’s amount, how much more money did Meili have than Jack?

[PapayaDad]

Cannot get round number leh…

My method:
Average = 28 coins
Total = 28 x 3 = 84 coins = $42

J+M=J+R+7 so M=R+7
R=4J

J=u
R=4u
M=4u+7
Total = 9u+7 = 42
u=3.8888?

[Chalupa]

(I need help for this question !) Mr. Lee left town at 6.45am and drove at a uniform speed of 60km/h to Town Q.Mrs Chen left town P at 7:15am and drove towards Town Q along the same expressway as Mr Lee.She passed him at 10:15am and continued driving at the same speed until she reached Town Q.The distance between Town P to Town Q was 560km.How far was Mr Lee from Town Q when Mrs Chen reached Town Q ?

Thanks in advance.

[PapayaDad]

Mr.Lee left town P at 6.45am? did u miss the P?


Also the correct thread for these is here :

http://www.kiasuparents.com/kiasu/forum/viewtopic.php?f=69&t=280&start=8950

[PapayaDad]

Mr Lee start 6.45 ; speed 60kmh

At 10.15 (3.5h later) ; Mr Lee travel 60+60+60+30=210km already

Mrs Chen took 3h (7.15 to 10.15) to travel 210km (catch up Mr Lee)
Mrs Chen Speen is 70kmh.
Mrs Chen need to travel another 350km to reach Q ie another 5h

Another 5h, Lee travel 300km only…still 50km away…

[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

[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

[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