Q&A - PSLE Math

[MathIzzzFun]

altp10:

tianzhu:

[quote=\"altp10\"]Hi Tianzhu,


It's from St. Andrews.. 1st time I encountered this.

How did u derive the 1 part---- 8?
And the 60?

I understand that since the sharing ratio is 5:3:4 it means it would be a multiple of 12. But is a little bit of guess and check involved to attain the 60?

Thank u.

Hi

Yes, you may use GC, but it tends to be less efficient especially at upper primary level.

A neat way to solve this question is to use MD.

Hope this helps.

Best wishes

http://farm9.staticflickr.com/8515/8575849299_dec8bcbc97_z.jpg\">

Hi Tianzhu,

Thanks alot... Very clear explaination..

Regards[/quote]There are multiple answers for this question. A similar question was discussed before on pg 806-

http://www.kiasuparents.com/kiasu/forum/viewtopic.php?f=69&t=280&start=8050

cheers

[ozora]

Need help to identify the number pattern below and find the missing

Number.

4, 6, 8, 12, 24, 36, ___,144, 480

[tianzhu]

ozora:

Need help to identify the number pattern below and find the missing

Number.

4, 6, 8, 12, 24, 36, ___,144, 480

Hi

The missing number is 96.

4*2 ----- 8
6*2 ----- 12
8*3 ------ 24
12*3 ----- 36
24*4 ------ 96
36*4 ------ 144
96*5 ------ 480

Hope this helps

Best wishes

[Jwoofamily]

Need help. From 2012 nanyang prelim.


At a swimming meet, school A had 18 more representatives than school B and 6 fewer representatives than school C. The ratio of the number of boys to girls from the three schools was 1:3. The ratios of the number of boys to the number of girls in schools A, B and C were 1:3, 1:5, 2:5 respectively. How many representatives from the three schools were there in all?

Answer in answer key is 96 but I don’t understand how they derive this answer.

Please help show detail workings.
Thanks.

[MathIzzzFun]

MathIzzzFun:

Treelodge:

http://i46.tinypic.com/idhth5.jpg\">

:?: Please help! :imdrowning:
Nanyang Prelim 2012 Q18 :slapshead:
Answer given = 96
:thankyou: :thankyou: :thankyou:

alternate approach using concept of multiples and a little Guess & Check..

School B, boys : girls --> 1 : 5 (total 6)
School A, boys : girls --> 1 : 3
School C, boys : girls --> 2 : 5
School A = School B + 18 = School B + 6 x 3
School C = School A + 6 = School B + 6 x 4
Total number of students in School B is a multiple of 6,
So, total number of students in School A is a multiple of 6 and total number of students in School C is also a multiple of 6

School C, boys : girls --> 2 : 5 --> 12 : 30
School A, boys : girls --> 1 : 4 --> 9 : 27 (6 less than C)
School B, boys : girls --> 1 : 5 --> 3 : 15 (18 less than A)
check --> boys: girls = (12+9+3) : (30+27+15) = 24:72= 1:3 √

So,
total number of students = 24 + 72 = 96

cheers.

Need help. From 2012 nanyang prelim.

At a swimming meet, school A had 18 more representatives than school B and 6 fewer representatives than school C. The ratio of the number of boys to girls from the three schools was 1:3. The ratios of the number of boys to the number of girls in schools A, B and C were 1:3, 1:5, 2:5 respectively. How many representatives from the three schools were there in all?

Discussed at pg 797 - see above

cheers

[tianzhu]

Jwoofamily:

Need help. From 2012 nanyang prelim.


At a swimming meet, school A had 18 more representatives than school B and 6 fewer representatives than school C. The ratio of the number of boys to girls from the three schools was 1:3. The ratios of the number of boys to the number of girls in schools A, B and C were 1:3, 1:5, 2:5 respectively. How many representatives from the three schools were there in all?

Answer in answer key is 96 but I don't understand how they derive this answer.

Please help show detail workings.
Thanks.

Hi

Here’s a solution posted earlier in this thread.

I think you can use MD, but I’ll use letters of the alphabet so as to save some time.

Number of representatives in B ------- 1 box
Number of representatives in A ------- 1 box + 18
Number of representatives in C ------- 1 box + 18 + 6

School A
Boys: Girls------- 1A:3A

School B
Boys: Girls ------- 1B:5B

School C
Boys: Girls ------- 2C:5C

1A + 1B + 2C ------ 1p
3A + 5B + 2C ------3p

3A + 3B +6C ------- 3p

3A + 3B +6C ------- 3A + 5B + 2C

Hence, you’ll get 1C ------- 2B

Now change (2C + 5C) to 14B and do a comparison.

14B – 6B (1B+5B) ------- 24

8B ------- 24

B ------- 3

C ------- 6

Number of representatives in C ------- 7*6 ------ 42

Number of representatives in A ------- 42 - 6 ------ 36

Number of representatives in B ------- 18

Total number ------- 96

Best wishes

[ozora]

tianzhu:

ozora:

Need help to identify the number pattern below and find the missing

Number.

4, 6, 8, 12, 24, 36, ___,144, 480

Hi

The missing number is 96.

4*2 ----- 8
6*2 ----- 12
8*3 ------ 24
12*3 ----- 36
24*4 ------ 96
36*4 ------ 144
96*5 ------ 480

Hope this helps

Best wishes

thanks. Really stuck.:)

[Oldschool]

Hi,


BTW, forum admins/mopderators might want to shift this thread under the relevant topics or header.

To begin,

(1) To complete the drawing,

Gogh + Picasso => 4 days, follow by
Picasso => 5 days

(2) Per day, G - P = 1/30 of the drawings

or G = P + 1/30

(3) Therefore, per day,

Gogh + Picasso complete => P + 1/30 + P of the drawings

4 days of (G + P) => 8P + 2/15
5 days of P => 5P

(4) 8P + 2/15 + 5P = 1 complete drawing

then P = 1/15
and G = 1/10

(5) Hence, Gogh will take 10 days whereas Picasso will take 15 days to completes the drawing alone.

Regards

[Oldschool]

Hi,


(1) 2 teams will take 30 days to complete.

Then, 30 days => 100%

So, in 6 days, the 2 teams completed => 100/30 x 6 = 20%

(2) Therefore, left with 80% which was completed by a single team in 40 days.

80% => 40 days
100% => 50 days

(3) Assume that both teams are equally hardworking. Then it would take 50 days for a single team to complete that certain job.

Regards

[MathIzzzFun]

Oldschool:

Hi,


(1) 2 teams will take 30 days to complete.

Then, 30 days => 100%

So, in 6 days, the 2 teams completed => 100/30 x 6 = 20%

(2) Therefore, left with 80% which was completed by a single team in 40 days.

80% => 40 days
100% => 50 days

(3) Assume that both teams are equally hardworking. Then it would take 50 days for a single team to complete that certain job.

Regards

the two team worked at different rate.

Total amount of work to be done --> 30 units (1 day = 1unit of work)

In 6 days, 6 units completed, 24 units left.

Team A (team remained to complete the work) takes 40 days to complete 24 units of work --> 24/40 unit/day = 0.6 unit/day

Team B --> (1 - 0.6) unit/day = 0.4unit /day

Number of days taken by each team to complete all the work by itself:
Team A --> 30/0.6 = 50 days
Team B --> 30/0.4 = 75 days

cheers.