Q&A - P4 Math

[mathnoobs]

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]

zeemimi:

mathnoobs:

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 ?

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]

mathnoobs:

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

[tianzhu]

mathnoobs:

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 ?

Hi

There was a similar type of question in one of the earlier posts.

Jane has some money. After spending $100 on 3 bags and 7 belts, she is short of $4 if she wants to buy another bag. However, if she buys 1 more belt, she will have $6 left.
a) How much does one bag cost? (Ans: $13)
b) How much does Jane have? (Ans: $109)

Please go to page 206 of this thread.
http://www.kiasuparents.com/kiasu/forum/viewtopic.php?f=71&t=6373&start=2050

Hope this helps.

Best wishes

[zeemimi]

mathnoobs:

zeemimi:

[quote=\"mathnoobs\"]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.[/quote]Sorry. i made a mistake in my model. Should be....

<------------ amt money siva has ------->
<--------$10----------->
|-------------------------|
<--------3WP7PC------->
___________________<---- cost of 1 WP------->
__________________________________<-0.40-> short
___________________<- 1PC-->
___________________________<-0.60-> extra

this is similar to the link given by tianzhu. the picture there speaks a thousand words! :salute:

$3 is derived by the difference between 1 WP and 1PC multiply by 3 because there are 3WP. $3 is not the remaining $. Sorry :slapshead:

I think you interpret $10 as the money Siva has. But $10 is the actual amt spent on 3WP 7PC.

[mathnoobs]

tianzhu:

mathnoobs:

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

ah.... I see. That makes sense. Thank you.

[mathnoobs]

zeemimi:

Sorry. i made a mistake in my model. Should be....


<------------ amt money siva has ------->
<--------$10----------->
|-------------------------|
<--------3WP7PC------->
___________________<---- cost of 1 WP------->
__________________________________<-0.40-> short
___________________<- 1PC-->
___________________________<-0.60-> extra

this is similar to the link given by tianzhu. the picture there speaks a thousand words! :salute:

$3 is derived by the difference between 1 WP and 1PC multiply by 3 because there are 3WP. $3 is not the remaining $. Sorry :slapshead:

I think you interpret $10 as the money Siva has. But $10 is the actual amt spent on 3WP 7PC.

I see. Yes, I did interpret $10 as the money Siva had. I see now that it is different. In that case, the $3 makes sense. Thank you.

[mathnoobs]

tianzhu:

mathnoobs:

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 ?

Hi

There was a similar type of question in one of the earlier posts.

Jane has some money. After spending $100 on 3 bags and 7 belts, she is short of $4 if she wants to buy another bag. However, if she buys 1 more belt, she will have $6 left.
a) How much does one bag cost? (Ans: $13)
b) How much does Jane have? (Ans: $109)

Please go to page 206 of this thread.
http://www.kiasuparents.com/kiasu/forum/viewtopic.php?f=71&t=6373&start=2050

Hope this helps.

Best wishes

thanks Tianzhu. The extra question will be useful for more drilling on this type of problems.

[tianzhu]

mathnoobs:

thanks Tianzhu. The extra question will be useful for more drilling on this type of problems.

Hi

You're welcome.

Best wishes

[jeestan]

P4 math dont need calculator right? My ds kept pestering me to get one because he said the teacher said they needed one.