Q&A - PSLE Math

[tianzhu]

Hi peggy


Where are your Q2 and Q3 from?

Q2)
As in any questions on Speed, it’s always useful to draw a time/distance line.

Alvin ------ Town P to Town Q
Simon ------ Town Q to Town P

For Simon, distance covered in 2h ------- 2*80 ------- 160km
160 + 40 ------- 200

Total time taken by Alvin ------ 6h (7am-1pm)
6 - 2 ------ 4

Alvin travelled 200km in 4h (7am-11am), hence his speed ------ 200/4 ------- 50km/h

2*50 ------- 100km
100/80 ------ 1.25 h

Simon ------- start @ 0945h from Town Q.

Q3)
In 1h the truck is faster than the van by 20km
In 6h the truck travels 120km more than the van.

Distance travelled by the van -------- 80 + 1 unit (distance travelled by the van in 6h)
Distance travelled by the truck ------- 1 unit + 120.

1 unit + 80 ------- 90%
1 unit + 120 ------- 100%

10% ------ 120 – 80 ------ 40
100% ------- 400

Distance between Town A and Town B ------- 400km

Speed of lorry ------ 400/6 ------- 66 2/3 km/h

Best wishes

[Zack7]

Hello in general, ratio problems are best approached by thinking in terms of fractions or models or algebra.


1) let the bigger number be x, smaller number be y

X+y = 5
X-y= 1

Solving, y=2, x =3
Now,
Xy = 24

This means there is a scaling of 4 . Since 2x3 is only 6. So to get 24, we scale the x and y values by 4. Remember that we are dealing with ratios.

So the bigger number is 12, the smaller is 8.




2) again, to simplify, just take it as 4 markers and 3 files were bought.

It cost 2 dollars for 4 markers, 1 dollar for 3 files.

This means 1marker cost 50cents and 1 file cost 33.3cents

1/2 : 1/3 is 3:2

[Bunny27]

tianzhu:

Hi peggy


Where are your Q2 and Q3 from?

Q2)
As in any questions on Speed, it’s always useful to draw a time/distance line.

Alvin ------ Town P to Town Q
Simon ------ Town Q to Town P

For Simon, distance covered in 2h ------- 2*80 ------- 160km
160 + 40 ------- 200

Total time taken by Alvin ------ 6h (7am-1pm)
6 - 2 ------ 4

Alvin travelled 200km in 4h (7am-11am), hence his speed ------ 200/4 ------- 50km/h

2*50 ------- 100km
100/80 ------ 1.25 h

Simon ------- start @ 0945h from Town Q.

Q3)
In 1h the truck is faster than the van by 20km
In 6h the truck travels 120km more than the van.

Distance travelled by the van -------- 80 + 1 unit (distance travelled by the van in 6h)
Distance travelled by the truck ------- 1 unit + 120.

1 unit + 80 ------- 90%
1 unit + 120 ------- 100%

10% ------ 120 – 80 ------ 40
100% ------- 400

Distance between Town A and Town B ------- 400km

Speed of lorry ------ 400/6 ------- 66 2/3 km/h

Best wishes

Hi, can someone help on this question:

1. At a carnival, 30% of the people are adults, 20% are girls and the rest are boys. After some adults have left, the percentage of adults at the carnival becomes 20%. How many adults have left the carnival?

:thankyou:

[Chenonceau]

My Question 1

http://i39.tinypic.com/e5jibm.png\">
http://i42.tinypic.com/2v7v6s8.jpg\">

Please help... Thank you.

[Chenonceau]

My Question 2

http://i44.tinypic.com/33msn7r.png\">

Thank you!

[tianzhu]

Chenonceau:

My Question 2

http://i44.tinypic.com/33msn7r.png\">

Thank you!

Hi

Good Morning.

Hope this helps.

Best wishes.

http://farm7.static.flickr.com/6070/6154555481_a1f43e1359_z.jpg\">

[Zack7]

Chenonceau:

My Question 1

http://i39.tinypic.com/e5jibm.png\">
http://i42.tinypic.com/2v7v6s8.jpg\">

Please help... Thank you.

wow kids these days learn crazy stuff... i learn these in secondary sch IIRC....


anyway

total volume of bottle = 6x6x32 + 18x12x12 = 3744

volume of 7/8 filled with water = 7/8 x 3744 = 3276

volume of water in the top cuboid = 3276 - 18x12x12 = 684

height of water level in the top cuboid = 684/36 = 19

height from the base of the bottle = 19 + 18 = 37cm

[peggy]

Hi Tianzhu,


The questions were shared with me by a friend’s DD enrichment class.

[tianzhu]

Chenonceau:

My Question 1

http://i39.tinypic.com/e5jibm.png\">
http://i42.tinypic.com/2v7v6s8.jpg\">

Please help... Thank you.

Hi

Where is this question from? It’s quite an interesting one.

Consider first the bigger cuboid of 12cm by 12 cm base and height 18cm.

Picture this,it is made up of 4 number of cuboid of 6cm by 6cm and height 18cm.

Total volume of water (8/8 or 8 units) --------- 5 number of cuboid of 6cm by 6cm and height 18cm plus one cuboid of 6cm by 6cm and height 14cm (18+14=32)

8 units ------ (5*18) + 14 ------ 104
7 units ------- 91

91 – 72 ------- 19

Water level from base of bottle ------- 18+19 ------- 37

Best wishes

[tianzhu]

Bunny27:

1. At a carnival, 30% of the people are adults, 20% are girls and the rest are boys. After some adults have left, the percentage of adults at the carnival becomes 20%. How many adults have left the carnival?

Hi

Please check your question.

I think some information might be missing.

Best wishes