Q&A - P5 Math

[MathIzzzFun]

YumYum:

Hi, can someone pl help with this qn (source: nanyang ca2, 2011):


Hanson had some one dollar coins and some fifty cent coins. The ratio of the number of one dollar coins to the number of fifty cent coins he had was 2:5. Hanson took 140 fifty cent coins to the bank and changed these fifty cent coins for the same value of one-dollar coins. In the end, the number of one-dollar coins to the number fifty cent coins he had became 5:2. Find the value of the fifty cent coins Hanson had at first.

Thanks.

Hi

this is a typical two-ratio problem sum and can be solved using cross-multiply or UP method.. hopefully these examples will help ...

http://www.flickr.com/photos/62167097@N02/6943541872/in/photostream

http://www.flickr.com/photos/62167097@N02/7069963797/in/photostream

http://www.flickr.com/photos/62167097@N02/6594157121/in/photostream

alternatively, the concept of same total value can be applied here since the total value of coins remains the same.

Value of $1 : $0.50 --> 2:1
At first, total value of $1: $0.50 --> 2 x 2 : 5 x 1 = 4 : 5
In the end, total value of $1:$0.50 --> 5 x 2 : 2 x 1 = 10 : 2
Total value is the same:
at first, value of $1 : $0.50 --> 16u : 20u
in the end, value of $1: $0.50 --> 30u : 6u
20u - 6u = 14u --> 140 x $0.50 = $70
1u --> $5
Initial value of 50-cent coins --> $5 x 20 = $100

cheers.

[YumYum]

Hi MathIzzzFun, thank you for the examples provided. Will go thru and Happy National Day!

[zinc6539]

Hi, could someone kindly help me solve this question from Nanyang Primary CA2 2011:


Yusof took 30 minutes to clean his father's car while his elder brother took 15 minutes to clean it. How long would both of them take to clean the car together?

The answer sheet stated 10 minutes. Can't figure out how they arrive at this answer.

Thanks in advance

[speedmaths.012624com]

zinc6539:

Hi, could someone kindly help me solve this question from Nanyang Primary CA2 2011:


Yusof took 30 minutes to clean his father's car while his elder brother took 15 minutes to clean it. How long would both of them take to clean the car together?

The answer sheet stated 10 minutes. Can't figure out how they arrive at this answer.

Thanks in advance

Hi,

In 30 min, Yusof can clean 1 car

In 15 min, his brother can clean 1 car
In 30 min, his brother can clean 2 cars

In 30 min, Yusof and his brother can clean 1 + 2 = 3 cars

3 cars in 30 min
1 car in 10 min.

Hope this helps.

Cheers


speedmaths.com

.

[the shadowed snake]

hi could someone help me

nanyang primary school p5 2011 paper 2 sa2 Q 18

http://test-paper.info/filemgmt_data/files/P5%20Maths%202011%20SA2%20Nanyang.PDF

[speedmaths.012624com]

the shadowed snake:

hi could someone help me

nanyang primary school p5 2011 paper 2 sa2 Q 18

http://test-paper.info/filemgmt_data/files/P5%20Maths%202011%20SA2%20Nanyang.PDF

Hi,

Q18.

When you see the words “at first” in the question (last sentence), it could be a “Work Backward” type of question. Not all the time, but in this case it is.

There were 280 tarts left.

Tarts in small boxes = 3/4 x 280 = 210 tarts
Before giving the 8 small boxes (or 8 x 7 = 56 tarts),
she would have 210 + 56 = 266 tarts

This is after selling half the small boxes

Before selling half the small boxes,
She would have 2 x 266 = 532 tarts

532 tarts were packed in 532/7 = 76 small boxes

Number of big boxes = 76 / 4 = 19 big boxes

Number of tarts in 19 big boxes = 19 x 10 = 190 tarts

Total number of tarts at first = 532 + 190 = 722 tarts

Hope this helps.

Cheers



speedmaths.com

.

[the shadowed snake]

speedmaths.com:

the shadowed snake:

hi could someone help me

nanyang primary school p5 2011 paper 2 sa2 Q 18

http://test-paper.info/filemgmt_data/files/P5%20Maths%202011%20SA2%20Nanyang.PDF

Hi,

Q18.

When you see the words “at first” in the question (last sentence), it could be a “Work Backward” type of question. Not all the time, but in this case it is.

There were 280 tarts left.

Tarts in small boxes = 3/4 x 280 = 210 tarts
Before giving the 8 small boxes (or 8 x 7 = 56 tarts),
she would have 210 + 56 = 266 tarts

This is after selling half the small boxes

Before selling half the small boxes,
She would have 2 x 266 = 532 tarts

532 tarts were packed in 532/7 = 76 small boxes

Number of big boxes = 76 / 4 = 19 big boxes

Number of tarts in 19 big boxes = 19 x 10 = 190 tarts

Total number of tarts at first = 532 + 190 = 722 tarts

Hope this helps.

Cheers



speedmaths.com

.

thanks but i can not understand the workings

[MathIzzzFun]

the shadowed snake:

hi could someone help me

nanyang primary school p5 2011 paper 2 sa2 Q 18

http://test-paper.info/filemgmt_data/files/P5%20Maths%202011%20SA2%20Nanyang.PDF

hope this helps...


In the end,
number of tarts in small boxes : big boxes = 3u :1u ** total 4u
Total number of tarts left = 240 --> 4u
tarts in small boxes --> 3/4 x 280 = 210
201/7 --> 30 boxes

so, before she gave 8 small boxes to friends,
number of small boxes --> 30 + 8 = 38

Since half of the small boxes were sold,
total number of small boxes, at first = 38 x 2 = 76

At first, there were 4 times as many small boxes as big boxes
so number of big boxes at first --> 76/4 = 19
Total number of tarts baked
= 76 x 7 + 19 x 10 = 722

cheers.

[the shadowed snake]

MathIzzzFun:

the shadowed snake:

hi could someone help me

nanyang primary school p5 2011 paper 2 sa2 Q 18

http://test-paper.info/filemgmt_data/files/P5%20Maths%202011%20SA2%20Nanyang.PDF

hope this helps...


In the end,
number of tarts in small boxes : big boxes = 3u :1u ** total 4u
Total number of tarts left = 240 --> 4u
tarts in small boxes --> 3/4 x 280 = 210
201/7 --> 30 boxes

so, before she gave 8 small boxes to friends,
number of small boxes --> 30 + 8 = 38

Since half of the small boxes were sold,
total number of small boxes, at first = 38 x 2 = 76

At first, there were 4 times as many small boxes as big boxes
so number of big boxes at first --> 76/4 = 19
Total number of tarts baked
= 76 x 7 + 19 x 10 = 722

cheers.

hi i do not understand this part
Total number of tarts left = 240 --> 4u
tarts in small boxes --> 3/4 x 280 = 210
201/7 --> 30 boxes
Total number of tarts baked
= 76 x 7 + 19 x 10 = 722

[MathIzzzFun]

the shadowed snake:

MathIzzzFun:

[quote=\"the hi could someone help me

nanyang primary school p5 2011 paper 2 sa2 Q 18

http://test-paper.info/filemgmt_data/files/P5%20Maths%202011%20SA2%20Nanyang.PDF

hope this helps...


In the end,
number of tarts in small boxes : big boxes = 3u :1u ** total 4u
Total number of tarts left = 240 --> 4u
tarts in small boxes --> 3/4 x 280 = 210
201/7 --> 30 boxes

so, before she gave 8 small boxes to friends,
number of small boxes --> 30 + 8 = 38

Since half of the small boxes were sold,
total number of small boxes, at first = 38 x 2 = 76

At first, there were 4 times as many small boxes as big boxes
so number of big boxes at first --> 76/4 = 19
Total number of tarts baked
= 76 x 7 + 19 x 10 = 722

cheers.

hi i do not understand this part
Total number of tarts left = 240 --> 4u
tarts in small boxes --> 3/4 x 280 = 210
201/7 --> 30 boxes
Total number of tarts baked
= 76 x 7 + 19 x 10 = 722

Can you solve this :
\"Melvin had thrice as many 50-cent coins as 20-cent coins. If he had a total 280 coins, how many 50-cent coins did he have ?\"

cheers.