Q&A - PSLE Math

[iamproudparents]

hi there anybody can advise?


1) in a party, there are 28 boys. 3/5 of the girls at the party wear spectacles. if 1/4 of the children at the party are girls who wear spectacles, how many children are there altogether at the party?

thanks

[PapayaDad]

1) in a party, there are 28 boys. 3/5 of the girls at the party wear spectacles. if 1/4 of the children at the party are girls who wear spectacles, how many children are there altogether at the party?


Total = 4u
girl wear spec = u

girl wear spec = 3p
girl no wear spec = 2p
girl total = 5p

girl wear spec = u = 3p
total = 4u = 12p

boys = 28
girls total = 5p
total = 12p = 28 + 5p
12p-5p=28
7p=28
p=4

total = 12p = 12 x 4 = 48

[Oldschool]

iamproudparents:

hi there anybody can advise?


1) in a party, there are 28 boys. 3/5 of the girls at the party wear spectacles. if 1/4 of the children at the party are girls who wear spectacles, how many children are there altogether at the party?

thanks

Hi,

Alternative - By fraction

3/5 of girls --> 1/4 of total
5/5 of girls --> 5/12 of total

So,

7/12 of total --> boys --> 28
12/12 --> (28/7) x 12 --> 48

Regards

[Emelyn]

PapayaDad:

80% of the spectators at a stadium were adults. 75% of the children at the stadium were boys. There were 36 more boys than girls.

(a) How many boys were there at the stadium ?
Boys=75%
Girls =25%
B - G = 75%-25% = 50% = 36
100% = 72
Boys = 75% of 72 = 54
Note : Girls = 18

(b) Some boys left the stadium and after which 10% of the remaining people at the stadium were boys. How many boys left the stadium ?
Children = 72 = 20%
Adult = 80% = 72 x 4 = 288
Girls = 18
Adult + Girls = 288 + 18 = 306 = 90%
10%=306/9=34 (boys)
20 boys left.

Hi PapayaDa, thanks very much.

Alamak... so straightforward, how come I didn't \"see\" it ??
Honestly, after doing so many questions with my son, my mind just refuse to think anymore.
I certainly do not have the same stamina as the kids !!

[mathnoobs]

MathIzzzFun:

mathnoobs:

Hi MathIzzzFun
I’m afraid I don’t quite understand how to simplify the following expression:
(18 units – 60km)/9units x 18
In your example, this will simplify to 36 units – 120 km
I’m stuck at how to eliminate the 9units from the denominator.

thanks

oops ... you are right..thanks for highlighting the error.. my apologies.
For this case, there will be no solution as the resultant quadratic equation will yield no real roots.

In order to get a real value for the speed, the question should be amended as follows:

Mr Tan travelled from Town A to Town B at 11:00. When he was 18 km from Town A , Mr Bala left Town B to Town A at a speed of 18km/h faster than Mr Tan. When Mr Bala reached Town A at 13:00, Mr Tan had completed 90 percent of his journey. What was Mr Tan's average speed?

in this case,
Mr Tan's speed --> 54 km/h and
Bala's speed --> 72 km/h

cheers.

thanks MathIzzzFun for the clarification. It is clearer now.

[elishatan]

Need help for 5 questions!


#1
http://elishatan.com/wp-content/uploads/2013/05/Evernote-Camera-Roll-20130506-142936-e1367824091265.jpg\">

#2
http://elishatan.com/wp-content/uploads/2013/05/Evernote-Camera-Roll-20130506-142928-e1367824147306.jpg\">

#3
http://elishatan.com/wp-content/uploads/2013/05/Evernote-Camera-Roll-20130506-142852-e1367824206891.jpg\">

#4
http://elishatan.com/wp-content/uploads/2013/05/Everno1te-Camera-Roll-20130506-142844-e1367824273638.jpg\">

[tianzhu]

elishatan:

Need help for 5 questions!


#1
http://elishatan.com/wp-content/uploads/2013/05/Evernote-Camera-Roll-20130506-142936-e1367824091265.jpg\">

Hi

This question has been discussed on page 204.

Best wishes

http://farm5.staticflickr.com/4152/5064543276_48eb65032a_z.jpg\">

http://farm5.staticflickr.com/4087/5063710027_2d395557a8_z.jpg\">

[tianzhu]

elishatan:

Need help for 5 questions!

#3
http://elishatan.com/wp-content/uploads/2013/05/Evernote-Camera-Roll-20130506-142852-e1367824206891.jpg\">

Hi

a) n*(n+1)/2 ----- number of unshaded triangles where n is the figure number

4*(4+1)/2 ---- 4*5/2 ------ 10

b )Number of unshaded triangles in figure 50 ------ 50*51/2 ------- 1275

c)number of shaded triangles ------ (n+1)*(n+2)/2

(n+1)*(n+2) ------ 4095*2 ------ 8190

With calculator, it's not too difficult to get 89 as the answer,

n ------ 89

Best wishes

[Oldschool]

elishatan:

Need help for 5 questions!


#2
http://elishatan.com/wp-content/uploads/2013/05/Evernote-Camera-Roll-20130506-142928-e1367824147306.jpg\">

Hi

Distance Ratio,
J : D
1/3 : 1/3 + 4.5
3/3 : 3/3 + 13.5

Time taken for John to reach the library is the same as time taken by David to reach the library plus time needed to travel another 13.5km.

Time taken by David to travel 13.5 km is
= 13.5 / 15 = 0.9 hrs = 54 mins

Since David reached library at 4.45pm, then

The time when John reach the library is 5.39pm

Regards

[Oldschool]

elishatan:

Hi

http://i40.tinypic.com/315e4j5.jpg\">

Regards