Q&A - PSLE Math

[Emelyn]

Hi,


Need help with the following questions from Nan Hua 2012 SA1 Maths :

Qn13 :
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 ?
(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 ?

Qn17 :
In a class library, there are some fiction and non-fiction books. If we remove 1 non-fiction book from the library, 1/7 of the remaining books are non-fiction books. If, instead of removing 1 non-fiction book, we remove 2 fiction books from the library, then 1/5 of the remaining books are non-fiction books. How many books are there in the class library ?

Many many thanks.

[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.

[PapayaDad]

in a class library, there are some fiction and non-fiction books. If we remove 1 non-fiction book from the library, 1/7 of the remaining books are non-fiction books. If, instead of removing 1 non-fiction book, we remove 2 fiction books from the library, then 1/5 of the remaining books are non-fiction books. How many books are there in the class library ?


f=6u
nf=1u + 1

6u-2=4nf
6u-2=4(1u+1)
6u-2=4u+4
2u=6
u=3

f=6u=18
nf=1u+1=4
total=22

[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
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#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

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