Q&A - PSLE Math

[lizawa]

[quote]Help needed for these 2 questions - many thanks in advance!

2. A block of wood 40cm by 14cm by 8 cm was cut into smaller pieces which were 7cm by 6cm by 2cm each. What was the maximum number of pieces that it could be cut into?[/quote]Need to maximize each side of the wood.

Place 7cm on the 14cm side. 2cm on the 8cm side. 6cm on the 40 cm side.

You get 2 *4 * 6 = 48

[MathIzzzFun]

Easy-going:

Beaker A and Beaker B contain some water. If 46.5ml of water is drained from Beaker A, the volume of the water in beaker A will be 60% that of the water in Beaker B.

If 35.2 ml of water is drained out from Beaker B, the volume of the water in Beaker B will be 85% that of the water in Beaker A.
What is the tota volume of water in Beaker and Beaker B?

hi

at first,
(add 46.5 ml back to Beaker A) Beaker A : Beaker B --> 3u + 46.5 : 5u

If 35.2ml drained from Beaker B,
Beaker A : Beaker B
--> 3u + 46.5 : 5u - 35.2 = 100 : 85 = 20 : 17

equalize/cross-multiply:
51u + 790.5 = 100u - 704
1u --> 30.5
Volume of water in
Beaker A --> 3 x 30.5 + 46.5 = 138 ml
Beaker B --> 5 x 30.5 = 152.5 ml

Total, Beaker A + Beaker B --> 290.5m

cheers.

[nounou]

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 bookmark costs 30 cents more than a sticker.
Number of bookmarks ------- 600/30 ------ 20
Therefore cost of 1 bookmark -------- 800/20 ------- 40 cents.\"

Can you please explain? :thankyou: :salute: :udaman:

tianzhu:

anneshirleygilbert:

Can somebody please help with this question?

Betina spent $20 on some stickers and bookmarks. She bought 6 times as many stickers as bookmarks. Each bookmark cost 30 cents more than a sticker. She spent $4 more on the stickers than on the bookmarks. What was the cost of a bookmark?

TIA.

Hi

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

She bought 6 times as many stickers as bookmarks.

Bookmarks ------ 1 unit
Stickers ------- 6 units

Hence, 1 unit of bookmark ------- 12/6 ------- 2

1 unit of bookmarks ------- 8

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

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

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

Check

120*10 ------- 1200
20*40 ------ 800

Best wishes

[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 bookmark 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]

jarenchuatw:

2. A block of wood 40cm by 14cm by 8 cm was cut into smaller pieces which were 7cm by 6cm by 2cm each. What was the maximum number of pieces that it could be cut into?

Hi

One way of looking at this question.

Hope this helps.

Best wishes

http://farm9.staticflickr.com/8001/7485835564_8dc81c8d0e_z.jpg\">

[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\">

[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.