Q&A - PSLE Math

[tianzhu]

bookwormkids:

Need help on the following questions.


1)
Log A and Log B are of different lengths. A carpenter wants to saw them into equal number of shorter pieces. The length of each piece from Log A need not be the same as that of each piece from Log B. If he saw Log A into 1.2m pieces and log B into 0.9m pieces, he has no leftover from log A but there will be 0.6m of log B left. If he saw Log A into 1.6m pieces and log B into 1.25m pieces, he has no leftover from log A but there will be 0.6m of log B left. Find the length of log A.

Hi

Please confirm from from your source.

There should be a difference in length.

Best wishes

[MathIzzzFun]

bookwormkids:

Need help on the following questions.


1)
Log A and Log B are of different lengths. A carpenter wants to saw them into equal number of shorter pieces. The length of each piece from Log A need not be the same as that of each piece from Log B. If he saw Log A into 1.2m pieces and log B into 0.9m pieces, he has no leftover from log A but there will be 0.6m of log B left. If he saw Log A into 1.6m pieces and log B into 1.25m pieces, he has no leftover from log A but there will be 0.6m of log B left. Find the length of log A.



Thanks.

Original question discussed at pg 801


http://www.kiasuparents.com/kiasu/forum/viewtopic.php?f=69&t=280&p=844766#p844766


cheers.

[tianzhu]

bookwormkids:

2)
Catherine has a box containing some black and white counters. When she adds in 15 white counters, 65% of the counters in the box are black. If she adds in another 40 black counters, 75% of the counters in the box are black. How many white counters are there in the box at first?

Hi

Scenario 1

When she adds in 15 white counters, 65% of the counters in the box are black.

White:Black ------ 7:13

Scenario 2

If she adds in another 40 black counters, 75% of the counters in the box are black.

Make the units for white counters for both scenarios the same.

White:Black ------ 1:3 -----7:21

21 – 13 ----- 8

8 units ---- 40

1 unit ----- 5

7 units ----- 35

35 – 15 ----- 20 (white counters@first)

Best wishes

[bookwormkids]

tianzhu:

bookwormkids:

2)
Catherine has a box containing some black and white counters. When she adds in 15 white counters, 65% of the counters in the box are black. If she adds in another 40 black counters, 75% of the counters in the box are black. How many white counters are there in the box at first?

Hi

Scenario 1

When she adds in 15 white counters, 65% of the counters in the box are black.

White:Black ------ 7:13

Scenario 2

If she adds in another 40 black counters, 75% of the counters in the box are black.

Make the units for white counters for both scenarios the same.

White:Black ------ 1:3 -----7:21

21 – 13 ----- 8

8 units ---- 40

1 unit ----- 5

7 units ----- 35

35 – 15 ----- 20 (white counters@first)

Best wishes

Hi Tianzhu, my son would like to know:

When 40 black counters are added, the number of white counters remain unchanged. So when 15 white counters are added,did the number of black counters remain the same?

Thanks for your time.

[bookwormkids]

MathIzzzFun:

bookwormkids:

Need help on the following questions.


1)
Log A and Log B are of different lengths. A carpenter wants to saw them into equal number of shorter pieces. The length of each piece from Log A need not be the same as that of each piece from Log B. If he saw Log A into 1.2m pieces and log B into 0.9m pieces, he has no leftover from log A but there will be 0.6m of log B left. If he saw Log A into 1.6m pieces and log B into 1.25m pieces, he has no leftover from log A but there will be 0.6m of log B left. Find the length of log A.


Thanks.

Original question discussed at pg 801


http://www.kiasuparents.com/kiasu/forum/viewtopic.php?f=69&t=280&p=844766#p844766


cheers.

Thank you MathIzzzFun and Tianzhu fpr your help.

[Beikiasu]

Hi, can someone help me to solve these problem sum?


1) A rectangular tank A, 180 cm by 60 cm by 80 cm, is 5/8 filled with water. When some water from tank A is pumped into another rectangular tank B, tank A is left with 15% of its water.
(a)How many litres of water is pumped into tank B? Ans:459 litres
(b)Given that tank B has a square base of sides 50 cm, what is the height of water in tank B? Ans:183.6 cm.SCG, 2011,SA1, Question 13, 4 mark.

2) Tina paid a total of $336 for 2 similar dresses and a skirt after a discount of 20% was given on the price of each item. If the original of each dress was 25% more than that of the original price the skirt, find the price of each dress before the discount. SCG, 2011, SA1, Question 12, 4 mark, Ans: $150.

3) Bemie and Ahmad shared the cost of a meal.Bemie paid $15. If Bermie paid $2 less, Ahmad would have had to pay 20% more. What was the cost of the meal? MGS, 2011, SA1, Question 3, 2 mark, Ans: $25.

Thanks

[tianzhu]

Beikiasu:

2) Tina paid a total of $336 for 2 similar dresses and a skirt after a discount of 20% was given on the price of each item. If the original of each dress was 25% more than that of the original price the skirt, find the price of each dress before the discount. SCG, 2011, SA1, Question 12, 4 mark, Ans: $150.

Hi

This question was discussed earlier in this thread.

This was my response.

You may use MD or work using units.

Original price of 2 similar dresses and a skirt ------- 420

1 dress ------ 5 units
1 skirt ------- 4 units

14 units ------- 420
1 unit ------- 30

Original price of dress ------- 5*30 -------150

Best wishes

[tianzhu]

Beikiasu:

3) Bemie and Ahmad shared the cost of a meal.Bemie paid $15. If Bermie paid $2 less, Ahmad would have had to pay 20% more. What was the cost of the meal? MGS, 2011, SA1, Question 3, 2 mark, Ans: $25.

Hi

Bernie ----- 15

If Bernie paid $2 less, Ahmad would have had to pay 20% more.

20% ----- 2

100% ------- 10

Cost of meal ----- 10+15 ----- 25

Actually, the numbers are pretty neat, students can easily arrive at the answer using GC.

Best answer.

[tianzhu]

bookwormkids:

Hi Tianzhu, my son would like to know:

When 40 black counters are added, the number of white counters remain unchanged. So when 15 white counters are added,did the number of black counters remain the same?

Thanks for your time.

Hi

I'll prepare the slide and give you the answer tomorrow.

Best wishes

[tianzhu]

Beikiasu:

Hi, can someone help me to solve these problem sum?

1) A rectangular tank A, 180 cm by 60 cm by 80 cm, is 5/8 filled with water. When some water from tank A is pumped into another rectangular tank B, tank A is left with 15% of its water.
(a)How many litres of water is pumped into tank B? Ans:459 litres
(b)Given that tank B has a square base of sides 50 cm, what is the height of water in tank B? Ans:183.6 cm.SCG, 2011,SA1, Question 13, 4 mark.

Hi

A rectangular tank A, 180 cm by 60 cm by 80 cm, is 5/8 filled with water.

5 units ----- 540 litres (180*80*60*5/8) (convert from cm3 to litres)

15% of 540 litres ------ 81 litres

Amount of water transferred to tank B ------ 540 – 81 ------ 459 litres

Height of water in tank B ------ 459000/50*50 ------ 183.6cm

Best wishes