Q&A - PSLE Math

[corneyAmber]

Dharma:

When distance is fixed; speed and time are inversely proportional.

Speed ratio => 80 : 60 = 4 : 3
Time ratio => 3: 4
4u – 3u = 1u = (3/4 – 1/3) = 5/12 hrs
Total distance = 80 x 3 x 5/12 = 100km
Time taken when speed is 90km/hr = 100/90 = 10/9 hrs

I like this shorter approach! :imcool:

[Dharma]

ksi:

Dharma:

When distance is fixed; speed and time are inversely proportional.

Speed ratio => 80 : 60 = 4 : 3
Time ratio => 3: 4
4u – 3u = 1u = (3/4 – 1/3) = 5/12 hrs
Total distance = 80 x 3 x 5/12 = 100km
Time taken when speed is 90km/hr = 100/90 = 10/9 hrs

I like this shorter approach! :imcool:

Glad you like it, ksi.

[KSP]

ksi:

KSP:

Hi need help here. Thanks.


Lily is meeting a friend at a certain time. If she drives at 80km/h, she will be 1/3 hr late. If she drives at 60km/h, she will be 3/4hr late. How long will the journey take if she drives at 90km/h?

Yo KSP! Why are you doing PSLE now? :?

i'm preparing myself ahead..... thanks.

[KSP]

Dharma:

ksi:

[quote=\"Dharma\"]When distance is fixed; speed and time are inversely proportional.

Speed ratio => 80 : 60 = 4 : 3
Time ratio => 3: 4
4u – 3u = 1u = (3/4 – 1/3) = 5/12 hrs
Total distance = 80 x 3 x 5/12 = 100km
Time taken when speed is 90km/hr = 100/90 = 10/9 hrs

I like this shorter approach! :imcool:

Glad you like it, ksi.[/quote]thanks to both of u...

[P5G]

Please help.


Paya Lebar Methodist Girls' Prelim Question 15.
http://www.orlesson.org/orp/09Ma/2009-P6-Math-SA2-PLMGS.pdf


The following pattern is created with 4 letters, A, B, C and D.

ABCDAABBCCDDAAABBBCCCDDD.................?
..............................................24th 230th

Following the above pattern, what is the 230th letter?

(1) A
(2) B
(3) C
(4) D


Given answer is (1).


TIA.

[MathIzzzFun]

P5G:

Please help.


Paya Lebar Methodist Girls' Prelim Question 15.
http://www.orlesson.org/orp/09Ma/2009-P6-Math-SA2-PLMGS.pdf


The following pattern is created with 4 letters, A, B, C and D.

ABCDAABBCCDDAAABBBCCCDDD.................?
..............................................24th 230th

Following the above pattern, what is the 230th letter?

(1) A
(2) B
(3) C
(4) D


Given answer is (1).


TIA.

Hi

The pattern can be grouped as follows:
group 1 (each letter appearing once) = ABCD
group 2 (each letter appearing twice) = AABBCCDD
and so forth

The total number of letters in each group will then be 4x1, 4x2, 4x3 etc..

To find the 230th letter, divide 230 by 4 = 57.5, so we need to find the group number n such that 1+2+3+4+...n is less than or equal to 57.5

1+2+3+4+5...+10 = 55

So, we know that 230th letter will be in group 11 ie each letter appearing 11 times,

4 x 55 = 220 (total number of letters in group 1 to group 10), 230 - 220 = 10, since A is the first letter, and each letter appears 11 times, the 10th letter in group 11 or the 230th letter is an \"A\"

cheers.

[fxchow]

Hi,


Can someone help in this question from Raffles Girls'Prm Sch-Prelim-Q18. TIA

There are more pupils in Sch A than Sch B.
30% of the pupils in Sch A is 45 more than 40% of the pupils in Sch B.
If 10% of the pupils in Sch A leaves to join Sch B, there will be 200 more pupils in Sch A than Sch B.

a) How many pupils are there in Sch B?
b) How many percent less pupils are there in Sch B than Sch A?
Leave your answer as fraction in the simplest form.

[small]

Hi fxchow,


HTH but I am not so sure on my answer for part (b).

a)
Given that 30% of the pupils in Sch A is 45 more than 40% of the pupils in Sch B.
0.3A - 45 = 0.4B --> x10

3A = 4B + 450 ----- equation (1)


If 10% of the pupils in Sch A leaves to join Sch B, there will be 200 more pupils in Sch A than Sch B
0.9A – 200 = 0.1A + 1B
0.8A = 1B + 200 --> x10

8A = 10B + 2000 ----- equation (2)


We will need to eliminate A to get B;

equation (1) x 8:
24A = 32B + 3600

equation (2) x 3:
24A = 30B + 6000

32B + 3600 = 30B + 6000
2B – 6000 – 3600
2B = 2400
1B = 1200

There are 1200 pupils in Sch B


b)
from equation (1) :

3A = 4 X 1200 + 450
3A = 4800 + 450
3A = 5250
1A = 1750 (100%)

The different between School A and School B is:
1750 – 1200 = 550

1750 = 100%
550 = 550/1750 x 100%
= 1100 / 35 %
= 31 3/7%


There are 31 3/7% percent less pupils in Sch B than Sch A

[MathIzzzFun]

fxchow:

Hi,


Can someone help in this question from Raffles Girls'Prm Sch-Prelim-Q18. TIA

There are more pupils in Sch A than Sch B.
30% of the pupils in Sch A is 45 more than 40% of the pupils in Sch B.
If 10% of the pupils in Sch A leaves to join Sch B, there will be 200 more pupils in Sch A than Sch B.

a) How many pupils are there in Sch B?
b) How many percent less pupils are there in Sch B than Sch A?
Leave your answer as fraction in the simplest form.

hi fxchow,

hope this helps

http://www.flickr.com/photos/62167097@N02/5842021695/in/photostream

cheers.

[fxchow]

small:

Hi fxchow,


HTH but I am not so sure on my answer for part (b).

a)
Given that 30% of the pupils in Sch A is 45 more than 40% of the pupils in Sch B.
0.3A - 45 = 0.4B --> x10

3A = 4B + 450 ----- equation (1)


If 10% of the pupils in Sch A leaves to join Sch B, there will be 200 more pupils in Sch A than Sch B
0.9A – 200 = 0.1A + 1B
0.8A = 1B + 200 --> x10

8A = 10B + 2000 ----- equation (2)


We will need to eliminate A to get B;

equation (1) x 8:
24A = 32B + 3600

equation (2) x 3:
24A = 30B + 6000

32B + 3600 = 30B + 6000
2B – 6000 – 3600
2B = 2400
1B = 1200

There are 1200 pupils in Sch B


b)
from equation (1) :

3A = 4 X 1200 + 450
3A = 4800 + 450
3A = 5250
1A = 1750 (100%)

The different between School A and School B is:
1750 – 1200 = 550

1750 = 100%
550 = 550/1750 x 100%
= 1100 / 35 %
= 31 3/7%


There are 31 3/7% percent less pupils in Sch B than Sch A

Hi Small,

Thank you for your solution, your answer b is correct.