## Q&A - PSLE Math

Academic support for Primary 6 and PSLE
Tang
BlueBelt
Posts: 297
Joined: Sat Jun 13,

### Re: Help to solve with a model method?

enoawng wrote:Mr Ng bought three times as many badges as toy cars and spent \$144 in total. He spent \$84 more on toy cars than on badges. Given that a toy car cost \$10.4 more than a badge, what was the cost of the bagde?
http://prischoolmaths.blogspot.com/sear ... hs-Decimal

James Ang
KiasuGrandMaster
Posts: 2200
Joined: Thu Jul 30,
Total Likes:1
Tang wrote:
James Ang wrote:There are 1000 lockers in a school with 1000 students. The first student opens all the lockers. The second student closes lockers 2,4,6,8,10 till 1000. The third student changes the state (close opened ones and open closed ones) of lockers 3,6,9,12 till 1000 . The fourth student changes the state of lockers 4,8,12,16 till 1000. How many lockers are opened in the end?
http://prischoolmaths.blogspot.com/2008 ... g_658.html
correct, solved this question more than 3 years ago in this tutorial.

http://www.jamesangtutors.com/articles/?type=read&id=11

Dharma
BlackBelt
Posts: 954
Joined: Mon Apr 06,

### Re: Help to solve with a model method?

enoawng wrote:Mr Ng bought three times as many badges as toy cars and spent \$144 in total. He spent \$84 more on toy cars than on badges. Given that a toy car cost \$10.4 more than a badge, what was the cost of the bagde?
Hi enoawng,

Hope this is useful

enoawng
OrangeBelt
Posts: 57
Joined: Tue Jul 28,

### Re: Help to solve with a model method?

Dharma wrote:
enoawng wrote:Mr Ng bought three times as many badges as toy cars and spent \$144 in total. He spent \$84 more on toy cars than on badges. Given that a toy car cost \$10.4 more than a badge, what was the cost of the bagde?
Hi enoawng,

Hope this is useful

Hi Dharma,

Isn't your method identical to using algebra if you define "1 part" to be the cost of the badge and "3units" to the number of badges

My understanding is that algebra is NOT allowed in PLSE. But if you replace algebra with units and parts, does that make it Ok for the examiners.

Please advise since algebra is taught is P6 but is not encourage for use in exams. Thats is my understanding.

Cheers Andrew

mathsparks
KiasuGrandMaster
Posts: 2825
Joined: Fri Mar 13,

### Re: Help to solve with a model method?

enoawng wrote:Hi Dharma,

Isn't your method identical to using algebra if you define "1 part" to be the cost of the badge and "3units" to the number of badges

My understanding is that algebra is NOT allowed in PLSE. But if you replace algebra with units and parts, does that make it Ok for the examiners.

Please advise since algebra is taught is P6 but is not encourage for use in exams. Thats is my understanding.

Cheers Andrew
Hi enoawng,
My son has been using combi of algebra/model in his p6 practice papers. Algebra IS allowed in PSLE, as long as clear working is shown on how the answer is derived and to define the variables used in the equation eg Let x be the no. of badges bought. Pls clarify with yr child's teacher and share with us his feedback.

kiasiparent
GreenBelt
Posts: 171
Joined: Sat Mar 21,
James Ang wrote:There are 1000 lockers in a school with 1000 students. The first student opens all the lockers. The second student closes lockers 2,4,6,8,10 till 1000. The third student changes the state (close opened ones and open closed ones) of lockers 3,6,9,12 till 1000 . The fourth student changes the state of lockers 4,8,12,16 till 1000. How many lockers are opened in the end?
Only 4 students are needed in this question. The other 996 students are redundant. I guess 1000 students is used so that the question will be even harder.

Dharma
BlackBelt
Posts: 954
Joined: Mon Apr 06,
Hi Andrew,

mathsparks is right.

enoawng
OrangeBelt
Posts: 57
Joined: Tue Jul 28,
Dharma wrote:Hi Andrew,

mathsparks is right.
Mr Ng bought three times as many badges as toy cars and spent \$144 in total. He spent \$84 more on toy cars than on badges. Given that a toy car cost \$10.4 more than a badge, what was the cost of the bagde?

Ok can anyone confirmed that this method below is allowed and the child will be awarded full marks?

Let N be the number of cars and B the cost of badge

3NB + N(B+10.4) = 144
N(B+10.4) -3NB = 84

Solving above
6NB = 144-84=60
NB=10

From 2nd statement
NB+10.4N-3NB = 84
10.4N= 84+20= 104
N=10; B=\$1

Also if we don't use Dharma's method or the algebric method, is there a model method?

Many thanks in advanced.

kiasiparent
GreenBelt
Posts: 171
Joined: Sat Mar 21,
Algebra are allowed in PSLE.

In fact, last year PSLE requires a lot on the use of algebra to answer a few questions. Other than using algebra, you can also use units and parts but that's actually algebra in disguise.

Other than that, You probably have to use guess and check.

Priskhipo
YellowBelt
Posts: 21
Joined: Sat Sep 13,
enoawng wrote:
Dharma wrote:Hi Andrew,

mathsparks is right.
Mr Ng bought three times as many badges as toy cars and spent \$144 in total. He spent \$84 more on toy cars than on badges. Given that a toy car cost \$10.4 more than a badge, what was the cost of the bagde?

Ok can anyone confirmed that this method below is allowed and the child will be awarded full marks?

Let N be the number of cars and B the cost of badge

3NB + N(B+10.4) = 144

N(B+10.4) -3NB = 84

Solving above
6NB = 144-84=60
NB=10

From 2nd statement
NB+10.4N-3NB = 84
10.4N= 84+20= 104
N=10; B=\$1

Also if we don't use Dharma's method or the algebric method, is there a model method?

Many thanks in advanced.

Here is the model method: