Q&A - PSLE Math

[CoffeeCat]

wkong:

Dear All,


Need help with the following question:

Shawn is late for school. His father, Mr. Wong, is driving him to school.

If Mr. Wong drives at 60km/h, Shawn will be 45 minutes late.
If Mr. Wong drives at 80km/h, Shawn will be 20 minutes late.

Find the distance from Shawn's house to his school.

Thanks in advance.

Hi, this is another typical inverse speed ratio question.
(Given constant distance)
Speed
60 : 80
3 : 4
Time Taken
4 : 3
(Given ratio of speed for 2 scenarios, the ratio for time taken is just the reverse for the 2 scenarios. Intuitively, for constant distance, the faster u travel, the lesser the amt of time u will take).
So 1 unit of time = 45-20= 25 mins.

[wkong]

CoffeeCat:

wkong:

Dear All,


Need help with the following question:

Shawn is late for school. His father, Mr. Wong, is driving him to school.

If Mr. Wong drives at 60km/h, Shawn will be 45 minutes late.
If Mr. Wong drives at 80km/h, Shawn will be 20 minutes late.

Find the distance from Shawn's house to his school.

Thanks in advance.

Hi, this is another typical inverse speed ratio question.
(Given constant distance)
Speed
60 : 80
3 : 4
Time Taken
4 : 3
(Given ratio of speed for 2 scenarios, the ratio for time taken is just the reverse for the 2 scenarios. Intuitively, for constant distance, the faster u travel, the lesser the amt of time u will take).
So 1 unit of time = 45-20= 25 mins.

So what's the answer? (distance)
Anders

[CoffeeCat]

wkong:

So what's the answer? (distance)
Anders

1 unit -> 25 mins
Assuming you looking at 60km/h scenario,
Time taken -> 4 units -> 100mins = 5/3 h
Hence Distance -> 5/3 * 60 = 100km

[wkong]

CoffeeCat:

wkong:

So what's the answer? (distance)
Anders

1 unit -> 25 mins
Assuming you looking at 60km/h scenario,
Time taken -> 4 units -> 100mins = 5/3 h
Hence Distance -> 5/3 * 60 = 100km

Thank you

[CoffeeCat]

Hifive:

Hi


Need help with this question:

http://www.flickr.com/photos/62186744@N04/5706093589/

Thanks in advance.

we are given
20% of A = 30% of C
Thus this is an equal concept question.
its better to convert and play with fractions so...
2/10 of A = 3/10 of C
There are different ways to find ratio of A to C, I make the numerator equal.
6/30 of A = 6/20 of C
hence
A : C
30 : 20
Note that shaded area of A = Shaded area of C = 6 units.
if 40% of B --> 6*2 = 12 units
then B -> 30 units
Total figure -> 30 + 30 + 20 - 12 = 68 units (the shaded area are double counted).
Fraction -> 12/68 = 3/17

[CoffeeCat]

Cheerfuldad:

Hi all,


Please help!

Q 1. While on a Europe tour, Sam read 544 pages of a book at first. He read the remaining pages in 23 days, with the same number of pages each day. During these 23 days, he read 1/13 of the book in 7 days. How many pages of the book did he read in the 7 days?



Q 2. There were 65 more boys than girls at a carnival on Sunday. 60% of the boys and 2/7 of the girls who were at the carnival on Sunday went on Saturday too. The remaining 143 boys and girls went only on Sunday.
a) How many more boys than girls went to the carnival on both days?
b) Find the total number of boys and girls at the carnival on Sunday.

Thank you.

Q1)
7 days -> 1/13 of book
1 day -> 1/91 of book
23 days -> 23/91 of book
Hence 68/91 of book -> 544 pages
book -> 544*91/68 = 728 pages
7 days -> 1/13 of book -> 728/13 = 56 pages

Q2)
One may use simultaneous eqns to solve...
let b and g represent the no. of boys and girls on sunday.
b = g+ 65
2/5 b + 5/7 g = 143
2/5 (g + 65) + 5/7 g = 143
26 + 39/35 g = 143
g = 117*35/39 = 105
b = 105 + 65 = 170
60% of boys -> 102
2/7 of girls -> 30
Difference 72
Total on Sunday -> 105 + 170 = 275

[Hifive]

CoffeeCat:

Hifive:

Hi


Need help with this question:

http://www.flickr.com/photos/62186744@N04/5706093589/

Thanks in advance.

we are given
20% of A = 30% of C
Thus this is an equal concept question.
its better to convert and play with fractions so...
2/10 of A = 3/10 of C
There are different ways to find ratio of A to C, I make the numerator equal.
6/30 of A = 6/20 of C
hence
A : C
30 : 20
Note that shaded area of A = Shaded area of C = 6 units.
if 40% of B --> 6*2 = 12 units
then B -> 30 units
Total figure -> 30 + 30 + 20 - 12 = 68 units (the shaded area are double counted).
Fraction -> 12/68 = 3/17

Hi CoffeeCat

Thanks for your explanation.

Regards

[tianzhu]

Hi


Hope this helps.

Please click at link to read question.

http://www.flickr.com/photos/62186744@N04/5706093589/

Best wishes.

http://farm4.static.flickr.com/3292/5708839634_c82f2e3e46_z.jpg\">

[Hifive]

Hi tianzhu


Thanks for your detailed explanation and the diagram helps in my understanding.

Cheers

[MathIzzzFun]

Cheerfuldad:

Hi all,


Please help!

Q 1. While on a Europe tour, Sam read 544 pages of a book at first. He read the remaining pages in 23 days, with the same number of pages each day. During these 23 days, he read 1/13 of the book in 7 days. How many pages of the book did he read in the 7 days?

Q 2. There were 65 more boys than girls at a carnival on Sunday. 60% of the boys and 2/7 of the girls who were at the carnival on Sunday went on Saturday too. The remaining 143 boys and girls went only on Sunday.
a) How many more boys than girls went to the carnival on both days?
b) Find the total number of boys and girls at the carnival on Sunday.

Thank you.

Hi Cheerfuldad,

A model approach to Q2 - http://www.flickr.com/photos/62167097@N02/5708623177/in/photostream

cheers.