## Q&A - P4 Math

ChiefKiasu
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### Q&A - P4 Math

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mathnoobs
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### Re: Q&A - P4 Math

let me start off with the first question for P4, this question seems incomplete as it made no mention that the jug was full in the first place and out of the full jug, 150ml of water was poured into the kettle, could we assume that ? If the jug was not full to start with, the 420ml information would be meaningless.

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A kettle could hold 420 ml more water than a jug. When 150ml of water was poured from the jug into the kettle, there were 4 times as much water in the kettle as the jug. How much water was there in the jug at first ?

tianzhu
Councillor
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### Re: Q&A - P4 Math

mathnoobs wrote:let me start off with the first question for P4, this question seems incomplete as it made no mention that the jug was full in the first place and out of the full jug, 150ml of water was poured into the kettle, could we assume that ? If the jug was not full to start with, the 420ml information would be meaningless.

----------------------------------------------------------------------------------
A kettle could hold 420 ml more water than a jug. When 150ml of water was poured from the jug into the kettle, there were 4 times as much water in the kettle as the jug. How much water was there in the jug at first ?
Hi

Good Morning

This question was discussed in one of the earlier posts in the P3/P4 Maths thread.

http://www.kiasuparents.com/kiasu/forum ... &start=460

Best wishes

mathnoobs
OrangeBelt
Posts: 74
Joined: Tue Aug 23,

### Re: Q&A - P4 Math

tianzhu wrote:
mathnoobs wrote:let me start off with the first question for P4, this question seems incomplete as it made no mention that the jug was full in the first place and out of the full jug, 150ml of water was poured into the kettle, could we assume that ? If the jug was not full to start with, the 420ml information would be meaningless.

----------------------------------------------------------------------------------
A kettle could hold 420 ml more water than a jug. When 150ml of water was poured from the jug into the kettle, there were 4 times as much water in the kettle as the jug. How much water was there in the jug at first ?
Hi

Good Morning

This question was discussed in one of the earlier posts in the P3/P4 Maths thread.

http://www.kiasuparents.com/kiasu/forum ... &start=460

Best wishes
thanks Tianzhu. It was very well presented. It's clear too me now. I had some comprehension issues with the problem statement, so it does not seem that the jug has to be full, nor the kettle has to be full.

tianzhu
Councillor
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### Re: Q&A - P4 Math

mathnoobs wrote: thanks Tianzhu. It was very well presented. It's clear too me now. I had some comprehension issues with the problem statement, so it does not seem that the jug has to be full, nor the kettle has to be full.
Hi

You're welcome.

Best wishes

mathnoobs
OrangeBelt
Posts: 74
Joined: Tue Aug 23,

### Re: Q&A - P4 Math

I've encountered this problem in a maths assessment book. However, I don't quite understand the solution. Hopefully, I'll get a better understanding here:
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Siva had some money. After spending \$10 on 3 writing pads and 7 penscils, he would be short of \$0.40 if he were to buy another writing pad. However, if he were to buy 1 more pencil, he would have \$0.60 left. How much did each writing pad cost ?

zeemimi
KiasuGrandMaster
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### Re: Q&A - P4 Math

mathnoobs wrote:I've encountered this problem in a maths assessment book. However, I don't quite understand the solution. Hopefully, I'll get a better understanding here:
--------------------------------------------------------------------------------------
Siva had some money. After spending \$10 on 3 writing pads and 7 penscils, he would be short of \$0.40 if he were to buy another writing pad. However, if he were to buy 1 more pencil, he would have \$0.60 left. How much did each writing pad cost ?
Using model method

<-----------------------\$10----------------->
|-------------------------|-------------------|
<--------3WP7PC-------><---remaining--->
___________________<---- cost of 1 WP------->
__________________________________<-0.40-> short
___________________<- 1PC-->
___________________________<-0.60-> extra
So cost of 1 WP is \$1 more than 1 PC

\$10-\$3=\$7 (\$3 is the remaining \$ after buying 3WP 7 PC)
\$7 / 10 = \$0.70
Cost of 1 WP = \$0.70 + \$1 = \$1.70

mathnoobs
OrangeBelt
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### Re: Q&A - P4 Math

the below question has been answered before in this forum, I understand the solution. However, my question is this phrase: "How many marbles did he have altogether?", how does one know if this refers to the number of marbles John had at first or John had at the end ? based on the solution, the question is asking for the marbles John had at first, but I find the question ambiguous. Would like to know how one deduce that the question is asking for marbles at the beginning or at the end.

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John has 1/3 as many red marbles as blue marbles. If he bought 12 red marbles, he would have 2/5 as many red marbles as blue marbles. How many marbles did he have altogether ?

mathnoobs
OrangeBelt
Posts: 74
Joined: Tue Aug 23,

### Re: Q&A - P4 Math

zeemimi wrote:
mathnoobs wrote:I've encountered this problem in a maths assessment book. However, I don't quite understand the solution. Hopefully, I'll get a better understanding here:
--------------------------------------------------------------------------------------
Siva had some money. After spending \$10 on 3 writing pads and 7 penscils, he would be short of \$0.40 if he were to buy another writing pad. However, if he were to buy 1 more pencil, he would have \$0.60 left. How much did each writing pad cost ?
Using model method

<-----------------------\$10----------------->
|-------------------------|-------------------|
<--------3WP7PC-------><---remaining--->
___________________<---- cost of 1 WP------->
__________________________________<-0.40-> short
___________________<- 1PC-->
___________________________<-0.60-> extra
So cost of 1 WP is \$1 more than 1 PC

\$10-\$3=\$7 (\$3 is the remaining \$ after buying 3WP 7 PC)
\$7 / 10 = \$0.70
Cost of 1 WP = \$0.70 + \$1 = \$1.70
thanks for the solution zeemimi.
However, I'm puzzled at the \$10-\$3 = \$7 part.
How do you deduce that \$3 is the remaining \$ after buying 3WP 7PC ?

I understand that the difference between WP and Pencil is \$1.00
4WP + 7P = 10 + 0.4
So using algebra, and let p = cost of pencil,
4p + 4 + 7p = 10 + 0.4
11p = 6.4
p = 0.58
I know p=0.58 is not the right answer, but I can't seem to see the error here.

tianzhu
Councillor
Posts: 3787
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### Re: Q&A - P4 Math

mathnoobs wrote:the below question has been answered before in this forum, I understand the solution. However, my question is this phrase: "How many marbles did he have altogether?", how does one know if this refers to the number of marbles John had at first or John had at the end ? based on the solution, the question is asking for the marbles John had at first, but I find the question ambiguous. Would like to know how one deduce that the question is asking for marbles at the beginning or at the end.

--------------------------------------------------------------------------------------
John has 1/3 as many red marbles as blue marbles. If he bought 12 red marbles, he would have 2/5 as many red marbles as blue marbles. How many marbles did he have altogether ?
Hi

Here, we are talking about the “if” concept. We are talking about an imagined scenario.

The word “if” signifies that the imagined scenario did not really happen.

So the total number of marbles in this case stays the same.

Best wishes