Q&A - P5 Math

[happyheart]

tianzhu:

happyheart:

I need help with this question please.


Q) A bus left the interchange with some passengers on board. At bus stop A, 10 passengers boarded the bus. When it reached bus stop B, 3/4 of the passengers alighted. The bus continued its journey and at bus stop C, 2/3 of the passengers alighted while 3 passengers boarded the bus. There were 18 passengers on the bus when it left bus stop C. How many passengers were on the bus when it left the interchange?

Hi

You may use a strategy called “Working backwards”.

A neat way is to break up the question into parts. You may use MD or units.

18 – 3 ------ 15

1 unit ------ 15

2 units ------ 30

45 passengers moved from B to C.

1 part ------ 45

3 parts ------ 135

Number of passengers moving from A to B -------- 45 + 135 ------- 180

At A, 10 passengers boarded.

Hence, number of passengers when leaving interchange ------- 180 – 10 ------ 170

Hope this helps.

Best wishes

Thank you, Tianzhu. My DS used branching method and he can derive the same answer for this question. Is there a risk in using branching for this type of Qns?

[tianzhu]

happyheart:

Thank you, Tianzhu. My DS used branching method and he can derive the same answer for this question. Is there a risk in using branching for this type of Qns?

Hi

You're welcome.

Whether MD, UM or BM, one should arrive at the same answer. Use the method the child is comfortable with.

Best wishes

[yxl]

Please help thanks


Mary spent $16.50 of her pocket money on a compact disc. She spent 1/5 of the remainder on a story book. She still had half of her money left.
a) How much was the storybook
b) How much was her pocket money?





Mark and rajah had a total of $60. After Rajah spent 1/3 of his money and mark spent $32, Mark had twice as much as Rajah. How much more money did Mark have than Rajah at first.

[MathIzzzFun]

yxl:

Please help thanks


Mary spent $16.50 of her pocket money on a compact disc. She spent 1/5 of the remainder on a story book. She still had half of her money left.
a) How much was the storybook
b) How much was her pocket money?

Hi
\"equal fraction\" method...


4/5 of remainder = 1/2 of pocket money
4/5 of remainder = 4/8 of pocket money

Remainder --> 5 units, story book --> 1 unit
pocket money --> 8 units
Compact disc --> 3 units = $ 16.50, 1 unit --> $5.50
Story book --> $ 5.50
pocket money --> 8 x $ 5.50 = $44.00

cheers.

[MathIzzzFun]

yxl:

Please help thanks


Mark and rajah had a total of $60. After Rajah spent 1/3 of his money and mark spent $32, Mark had twice as much as Rajah. How much more money did Mark have than Rajah at first.

After spending,
Rajah --> 2 units
Mark --> 4 units

At first,
Rajah --> 3 units
Mark --> 4 units + $32
Total --> 7 units + $32 = $60, 1 unit --> $4

4 units + $32 (Mark) - 3 units (Rajah) --> 1 unit + $32 = $36
Mark had $36 more that Rajah at first.

cheers.

[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.

[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

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