Q&A - PSLE Math

[jarenchuatw]

Thanks BB, but could u explain how did u derive the below equation

SR:SC
9:12

How did u derive this equation?

Common distance question. Use ratio of speed and time to solve
TR : TC
12 : 9
SR : SC
9 : 12

3u -> 15
1u -> 5
speed of Rani -> 5 * 9 = 45 km/h
Distance = 45 * 12 = 540 km

Speed of chua -> 12 * 5 = 60km/h

[2632parent]

1) A car left Town A For Town B. At the same time a lorry left Town B for Town A. The average speed of the car was 90km/h while the speed of the lorry was 70km/h. The two vehicles passed each other at a point 36km away from the mid point between Town A and Town B. What was the distance between Town A and Town B?



2) Wendy had 80 more stamps than Mary but 50 more stamps than Jean. Wendy gives 1/2 of her stamps to Mary. Then Mary gives 1/5 of her stamps to Jean . If Jean has 62 more stamps than Wendy, how many stamps does Mary have in the end ?

:?:

[lizawa]

jarenchuatw:

Thanks BB, but could u explain how did u derive the below equation

SR:SC
9:12

How did u derive this equation?

Common distance question. Use ratio of speed and time to solve
TR : TC
12 : 9
SR : SC
9 : 12

3u -> 15
1u -> 5
speed of Rani -> 5 * 9 = 45 km/h
Distance = 45 * 12 = 540 km

Speed of chua -> 12 * 5 = 60km/h

Time is inversely proportional to speed, given that distance is common. So if ratio of speed is 12:9 then ratio of time will be 9:12

[MathIzzzFun]

2632parent:

1) A car left Town A For Town B. At the same time a lorry left Town B for Town A. The average speed of the car was 90km/h while the speed of the lorry was 70km/h. The two vehicles passed each other at a point 36km away from the mid point between Town A and Town B. What was the distance between Town A and Town B?



2) Wendy had 80 more stamps than Mary but 50 more stamps than Jean. Wendy gives 1/2 of her stamps to Mary. Then Mary gives 1/5 of her stamps to Jean . If Jean has 62 more stamps than Wendy, how many stamps does Mary have in the end ?

:?:

Hi

Q1.

http://i45.tinypic.com/raafk1.png\">

Q2.
Mary’s stamps --> 10 units
Wendy’s stamps --> 10 units + 80
Jean’s stamps --> 10 units + 30

After Wendy’s gave ½ her stamps to Mary,
½ Wendy’s stamps --> 5 units + 40
Mary’s stamps --> 15 units + 40 ---- ⅕ of Mary’s stamps --> 3 units + 8

After Mary gave ⅕ of her stamps to Jean,
Mary’s stamps --> 12 units + 32
Jean’s stamps --> 13 units + 38

In the end, Jean had 62 more stamps than Wendy,
13 units + 68 = 5 units + 40 + 68
1 unit --> 8

In the end, Mary’s stamps --> 12 x 8 + 32 = 128

cheers.

[corneyAmber]

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[MathIzzzFun]

mistychances:

Hi, saw this worked example in My Pals are Here.


Do not understand why the ''crooked'' path is being calculated as a straight path. Isn't a crooked one longer than a straigth one?

Will appreciate if someone can help to explain to me. Thank You

http://i47.tinypic.com/4jipk.jpg\">

area of a parallelogram of height H, and base B has the same area as a rectangle of height H, and length B but the perimeter of same parallelogram is longer than that of the rectangle.

cheers.

[mistychances]

Sorry Moderator Will watch out the next time.


Thank you very much Math Izzz Fun Now I get the picture

[2632parent]

Sorry class monitor, I will be more careful in future. :imsorry:

[nounou]

Kindly include explanation as well. Can't understand the working :gloomy: :stupid: :imdrowning: :imsorry:


Many thanks X 100000000000000 :?:
:thankyou:
:salute:

tianzhu:

Treelodge:

Dear Tianzhu, HELP please! :?:

:? I don't understand \"Hence, 1 unit of bookmark ------- 12/6 ------- 2
1 unit of bookmarks ------- 8
There is an extra of 6 (8-2) because the bookma
rk costs 30 cents more than a sticker.
Number of bookmarks ------- 600/30 ------ 20
Therefore cost of 1 bookmark -------- 800/20 ------- 40 cents.\"

Hi

I am sorry for the error.

It should be read as 1 unit of stickers instead of bookmarks.

I'll revise the original post.

Please draw out the MD as it gives a clearer picture.

Best wishes

[tianzhu]

Treelodge:

Kindly include explanation as well. Can't understand the working :gloomy: :stupid: :imdrowning: :imsorry:

Many thanks X 100000000000000 :?:
:thankyou:
:salute:

Hi

Good Morning.

My earlier response to anneshirleygilbert’s question was an attempt to break down the question for her to draw out the MD.

I’ll attempt to further break down the question into smaller parts.

Betina spent $20 on some stickers and bookmarks. She spent $4 more on the stickers than on the bookmarks.

This gives us,

Amount spent on stickers ------ 12
Amount spent on bookmarks ------- 8

Please draw the MD.

She bought 6 times as many stickers as bookmarks.

Bookmarks ------ 1 box
Stickers ------- 6 boxes

The amount spent on stickers is shown by 6 boxes.

Hence, 1 box of stickers ------- 12/6 ------- 2

The amount spent on bookmarks is shown by 1 box + an amount equal to (8 – 2).

There is an extra of 6 (8-2) because the bookmark costs 30 cents more than a sticker.

From here, we are able to calculate the number of bookmarks.

Number of bookmarks ------- 600/30 ------ 20

Therefore cost of 1 bookmark -------- 800/20 ------- 40 cents.

Best wishes