Q&A - PSLE Math

[Oldschool]

Musicstar:

Thank you Tianzhu for posting the \"If\" questions.


I have been trying to do all these questions but has been stucked in question 1 already. Would you mind to enlighten me. Thank you. Are these questions which already been posted ?

YumYum:

[quote=\"tianzhu\"]Questions involving “Two ifs” or “Double if ”

Questions on “Two ifs” or “Double if ” are commonly found in past years test papers.

This question posted by Musicstar is certainly an interesting one.

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?

I’ll use it as an illustration. Please refer to attached slide.

I’ve also spent some time to dig out some questions on “DI” in KSP so that students can have some easy reference.

Hope this helps.

Best wishes

Questions on DI (KSP)

1) Jack and Aqil had some game cards. If Jack gave Aqil 52 cards, he would have the same number of cards as Aqil. If Aqil gave Jack 34 cards, the ratio of the number of cards Aqil had to the number of cards Jack had would be 3:7.How many cards did Jack have at first?(267)

2) If Ahmad gives Pillay 17 marbles, the ratio of his marbles to that of Pillay's will be 4:7. If Ahmad gives Pillay 5 marbles, both will have the same number of marbles. How many marbles does Ahmad have?(49)

3) Ben and Marcus received some money from their mother. Marcus would have $64 more than Ben if Ben gave 2/5 of his share to Marcus. Marcus would have $144 more than Ben if Ben gave 2/3 of his share to Marcus. How much money did Ben receive from his mother?(150)

4) Bottle A and bottle B both contain some juice.
If 1.3 litre of juice was poured into bottle A, the volume of juice in A will be 1.6 times that of the volume of the juice in bottle B.
If 480 ml of juice was poured into bottle B, the volume of juice in bottle B will be 1.8 times that of the volume of the juice in bottle A.
(a) What is the volume of juice in bottle A? (Ans. 1.1 litre)
(b) what is the difference in the volume of juice in both bottles? (Ans: 0.4 litre)

5) Mrs Tan has some pencils. If she packs them into bundles of 5 pencils in each bundle, she will have 4 extra pencils. If she packs them into bundles of 9 pencils in each bundles, she will need 7 more pencils. How many pencils are there? (29)

6) Keith and Shawn each have some money. If Keith spends $38, the ratio of the amount of money Keith has to the amount of money Shawn has will become 2:5. If Shawn spends $38, the ratio will become 8:13. How much money does each boy have? (152,285)

7) Susan has some vanilla and chocolate sweets in her bag. If she adds 20 vanilla sweets into the bag, the percentage of vanilla sweets in the bag becomes 40%. If she adds 30 chocolate sweets, there will be 70% of chocolate sweets in the bag. How many vanilla and chocolate sweets does she have?(210)

If Sam gives Terry $350, he will have 4 times as much money as Terry. If Sam gives Terry $550, he will have thrice as much money as Terry. How much money does Sam have ?(3200)

9) Alicia and Bruce are given some money each. If Alicia spends three times as much as Bruce, She will have $1000 more when Bruce has spent all his money. If Alicia spends half of what Bruce spends, she will have $2200 when Bruce has spent all his money. What is the total sum of money given to Alicia and Bruce? (2440 ,480)

10) Jack and Jill owned a chicken farm each. If Jack and Jill sold 60 chickens and 30 chickens respectively in a day, Jack would have 300 chickens left when Jill has sold all her chickens. If Jack sold 30 chickens a day and Jill sold 60 chickens a day, Jack would have 930 chickens left when Jill has sold all her chickens. Find the number of chickens Jack has on his farm. (1140)

11) Tammy and Sharon have some money. If Tammy spent $60 each day and Sharon spent $30 each day, Tammy is left with $400 when Sharon spent all her money. If Sharon spent $60 each day and Tammy spent $30 each day, Tammy is left with $1150 when Sharon spent all her money. How much money do the two girls have? (1900)

12) Sonia has some money to buy some photo albums and photo frames.
If she buys 7 similar photo albums and 3 similar photo frames, she will be short of $27.10.
If she buys 2 similar photo albums and 5 similar photo frames, she will have $19 left.
If a photo frame costs $8.20, how much money does Sonia have?(85)

http://farm9.staticflickr.com/8248/8665075086_b33349a259_z.jpg\">

Hi Tianzhu,

Thank you for compiling the 'If' questions, they are very useful. thks for yr kind thoughts. :thankyou:

[/quote]
Hi,

Just like to share,

The example given is a \"DI\" question but the 2nd event is a continuous from the 1st event.

The question is also a \"DI\" problems but both events are separated.

Therefore, though both are \"DI\" problems but one need to ask
(a) one continuous event ? or
(b) two separate events ?

Alternatively, you can also make use of \"total unchanged\" (depending on question).

http://www.flickr.com/photos/94858125@N03/8671339014/sizes/m/in/photostream/

Regards

[superksmum]

Hi can someone please help on these 2 questions:


1) Alan and Charlie received some money from their mother. Charlie would have $32 more than Alan if Alan gave 2/5 of his share to Charlie. Charlie would have $96 more than Alan if Alan gave 2/3 of his share to Charlie. How much money did they receive from his mother?

2) Primary 6A has 30 pupils while Primary 6B has 35 pupils. The pupils in both classes took the same Math Test and they scored an average of 80 marks. The average score of Primary 6A was 13 marks lower than that of Primary 6B. find the average score of Primary 6A.

Thank you.

[MathIzzzFun]

superksmum:

Hi can someone please help on these 2 questions:


1) Alan and Charlie received some money from their mother. Charlie would have $32 more than Alan if Alan gave 2/5 of his share to Charlie. Charlie would have $96 more than Alan if Alan gave 2/3 of his share to Charlie. How much money did they receive from his mother?


Thank you.

At first, Alan's money --> 15 units (LCM of 3 &5)

If Alan gave 2/5 of his money = 6 units, to Charlie, Charlie would have $32 more than Alan:

Alan's money left --> 9 units
Charlie's money left --> 9 units + $32

At first,
Charlie's money --> 3 units +$32
Alan's money --> 15 units

If Alan gave 2/3 of his share = 10 units, to Charlie, Charlie would have $96 more than Alan,

Alan's money left --> 5 units
Charlie's money --> 13 units + $32

13 units + $32 = 5 units + $96
8 units --> $64, 1 unit --> $8

Charlie's money --> 3 x $8 $32 = $56
Alan's money --> 15 x $8 = $120

cheers.

[superksmum]

MathIzzzFun:

superksmum:

Hi can someone please help on these 2 questions:


1) Alan and Charlie received some money from their mother. Charlie would have $32 more than Alan if Alan gave 2/5 of his share to Charlie. Charlie would have $96 more than Alan if Alan gave 2/3 of his share to Charlie. How much money did they receive from his mother?


Thank you.

At first, Alan's money --> 15 units (LCM of 3 &5)

If Alan gave 2/5 of his money = 6 units, to Charlie, Charlie would have $32 more than Alan:

Alan's money left --> 9 units
Charlie's money left --> 9 units + $32

At first,
Charlie's money --> 3 units +$32
Alan's money --> 15 units

If Alan gave 2/3 of his share = 10 units, to Charlie, Charlie would have $96 more than Alan,

Alan's money left --> 5 units
Charlie's money --> 13 units + $32

13 units + $32 = 5 units + $96
8 units --> $64, 1 unit --> $8

Charlie's money --> 3 x $8 $32 = $56
Alan's money --> 15 x $8 = $120

cheers.

:thankyou:

[MathIzzzFun]

superksmum:

Hi can someone please help on these 2 questions:


2) Primary 6A has 30 pupils while Primary 6B has 35 pupils. The pupils in both classes took the same Math Test and they scored an average of 80 marks. The average score of Primary 6A was 13 marks lower than that of Primary 6B. find the average score of Primary 6A.

Thank you.

http://i34.tinypic.com/npnw8x.png\">

cheers.

[superksmum]

MathIzzzFun:

superksmum:

Hi can someone please help on these 2 questions:


2) Primary 6A has 30 pupils while Primary 6B has 35 pupils. The pupils in both classes took the same Math Test and they scored an average of 80 marks. The average score of Primary 6A was 13 marks lower than that of Primary 6B. find the average score of Primary 6A.

Thank you.

http://i34.tinypic.com/npnw8x.png\">

cheers.

:thankyou:

[ozora]

tianzhu:

ozora:

Need help:

q1) Doreen n Joyce started jogging at 7 am round 400m track. Doreen stopped jogging at 7.20am. By then, Joyce covered 2/3 of the distance completed by Doreen. Doreen ave speed was 30m/min faster than Joyce. How many rounds of track had each of them completed?

Hi

Distance ratio

Doreen:Joyce ---- 3:2

Speed ratio

Doreen:Joyce ---- 3:2

1 unit ------ 30 m/min

Doreen’s speed ------- 3*30 ------ 90 m/min

Joyce’s speed -------- 60 m/min

In 20 minutes

Doreen ------- 90*20 ------- 1800

1800/400 ------- 4 ½ rounds

Joyce -------- 60*20 ------- 1200

1200/400 ------- 3 rounds

Best wishes

thanks for teaching alt method

[ozora]

Need help in speed question.

The distance between town A and town B is 180km.
A van travelled from Town A at 1130am to town B.
1/2h later, a car travelled from town A to town B at an average speed of 75km/h.
The car overtook the van and reached town B first. The van reached town B at 2.30pm.
A) at what time did the car overtake the van?
B) how far away was the van from town B when the car reached town B?

[Oldschool]

ozora:

Need help in speed question.

The distance between town A and town B is 180km.
A van travelled from Town A at 1130am to town B.
1/2h later, a car travelled from town A to town B at an average speed of 75km/h.
The car overtook the van and reached town B first. The van reached town B at 2.30pm.
A) at what time did the car overtake the van?
B) how far away was the van from town B when the car reached town B?

Hi,

Speed of Van = 180 / 3 = 60km/h

a) At the time of overtaking, both Van and Car have travelled the same distance,

60(t) = 75 (t - 1/2)
t = 2.5 hrs

So, the time is 1400 hrs or 2pm when the Car overtakes the Van.

b) Time taken for Car to reach B = 180 / 75 = 2.4hrs

In (2.4+0.5) hrs, the Van travelled = 60 x (2.9) = 174km

Thus, the Van is 180-174=6 km away from B


Note: My error for 2nd part, instead of 2.4, it should be 2.9hrs


Regards

[ozora]

Oldschool:

ozora:

Need help in speed question.

The distance between town A and town B is 180km.
A van travelled from Town A at 1130am to town B.
1/2h later, a car travelled from town A to town B at an average speed of 75km/h.
The car overtook the van and reached town B first. The van reached town B at 2.30pm.
A) at what time did the car overtake the van?
B) how far away was the van from town B when the car reached town B?

Hi,

Speed of Van = 180 / 3 = 60km/h

a) At the time of overtaking, both Van and Car have travelled the same distance,

60(t) = 75 (t - 1/2)
t = 2.5 hrs

So, the time is 1400 hrs or 2pm when the Car overtakes the Van.

b) Time taken for Car to reach B = 180 / 75 = 2.4hrs

In 2.4hrs, the Van travelled = 60 x 2.4 = 144km

Thus, the Van is 180-144=36 km away from B

Regards

thanks got it correct the first part but should the answer in b) 6 km as the van has travelled extra of 0.5h