Q&A - PSLE Math

[lantian]

There are three conditions which will give the same average number. First case, A is greater than B. Second case, B is greater than A. In the last case, A is equal to B. It’s not illogical to assume that A has the same value as B. After going through with my son, we chose to use the last scenario to show as the model for our solution.


You may choose to represent your solution in a different way

http://farm4.static.flickr.com/3265/2901723766_130f7070f2_o.jpg\">

[heutistmeintag]

My son came back today with this PSLE question btw I am not sure if he had recalled the full question.


Brian invited some boys and girls, there are 20 more boys than girls. 3/4 of the boys and 2/3 of the girls managed to come, how many children did Brian invite?

I cant figure this out because there seems to be too little info to work with. For example the 2nd statement doesnt provide a mathematical relationship.

[kiasuson]

According to my son, another information given is that there are 19 children that did not turn up.

[kiasuson]

My son’s answer is 68 and I think he is correct.

[heutistmeintag]

oh i see, now I can solve by alegbra.


B=20+G

1/3G+1/4B=19
4G+3B=19*12=228
4G+3*(20+G)=228
4G+60+3G=228
7G=228-60
7G=168
G=24
B=20+24=44
Total number of children invited is (24+44)=68

ok, can someone explain using modelling?

[heutistmeintag]

kiasuson:

My son's answer is 68 and I think he is correct.

Thanks for providing the missing link. Happy for your son but sad for mine, he didnt get it.

[lizawa]

heutistmeintag:

oh i see, now I can solve by alegbra.


B=20+G

1/3G+1/4B=19
4G+3B=19*12=228
4G+3*(20+G)=228
4G+60+3G=228
7G=228-60
7G=168
G=24
B=20+24=44
Total number of children invited is (24+44)=68

ok, can someone explain using modelling?

Solve by model :
--------------------
Boys : 12u + 20
Girls : 12u

1/4 boys did not come -> 3u + 5 (you can break 20 into 4 parts, each part is 5)
1/3 girls did not come -> 4u

7u + 5 = 19
1u = 2
Altogether -> 24u + 20 = 48+20 = 68.

[kiasuson]

Anymore interesting questions that were feedback from the children? My son said the paper was ok as expected…

[raysusan]

lizawa:

heutistmeintag:

oh i see, now I can solve by alegbra.


B=20+G

1/3G+1/4B=19
4G+3B=19*12=228
4G+3*(20+G)=228
4G+60+3G=228
7G=228-60
7G=168
G=24
B=20+24=44
Total number of children invited is (24+44)=68

ok, can someone explain using modelling?

Solve by model :
--------------------
Boys : 12u + 20
Girls : 12u

1/4 boys did not come -> 3u + 5 (you can break 20 into 4 parts, each part is 5)
1/3 girls did not come -> 4u

7u + 5 = 19
1u = 2
Altogether -> 24u + 20 = 48+20 = 68.

is this the Q47?

[lizawa]

raysusan:

lizawa:

[quote=\"heutistmeintag\"]oh i see, now I can solve by alegbra.


B=20+G

1/3G+1/4B=19
4G+3B=19*12=228
4G+3*(20+G)=228
4G+60+3G=228
7G=228-60
7G=168
G=24
B=20+24=44
Total number of children invited is (24+44)=68

ok, can someone explain using modelling?

Solve by model :
--------------------
Boys : 12u + 20
Girls : 12u

1/4 boys did not come -> 3u + 5 (you can break 20 into 4 parts, each part is 5)
1/3 girls did not come -> 4u

7u + 5 = 19
1u = 2
Altogether -> 24u + 20 = 48+20 = 68.

is this the Q47?[/quote]Hi raysusan,

I don't think so. Q47 should be a 5-mark question. This doesn't look like a 5-mark question to me.