Q&A - PSLE Math

[atutor2001]

worridaddy:

Hi can anyone help :

When Larry's age was twice Henry's age, Don's age was 27. When Don's age was twice Larry's age, Henry's age was 15. What was Henry's age when Don was 58 years old ?
Thanks ! :?

This question use model very confusing.
Use units with \"difference in age never change\" and simultaneous, is easier.
So the easy way is :

L... H... D
2u. u... 27
v.. 15.. 2V
.... ? ... 58

Difference in age never change :
2u-u = v-15 that is u = v-15 ...... Eqn (1)
u-27 = 15-2v that is u = 42-2v ......Eqn (2)

Solving (1) & (2) :
v-15 = 42-2v
3v = 57
v = 19
2v = 38

58-38 = 20
15+20 = 35 (answer)

Easier if Pr kids learn simult eqns - most of them can

If die die must draw model, then draw comparison models for

u+15 is same length as v .....1st comparison model
u+2v is same length as 42....2nd comparison model

then replace the \"2v\" in the 2nd model with 2u+30

[worridaddy]

Thanks atutor2001.

[atutor2001]

worridaddy:

Thanks atutor2001.

You are most welcome, strongly recommend to teach simult eqns to pr school students. It makes solving problem sum much easier.

[chrisu]

Thanks to all for responding to this post. My daughter came back yesterday evening and told me that the teacher and the Maths HOD agreed to accept both 225 and 450 as answer since the question is ambiguous.


The answer is 225 if comparison is made after the 1/3 and 1/5 is given to Rahmad. The answer will be 450 if the comparison is made before the 1/3 and 1/5 is given to Rahmad.

As for proving of Adam = 450;
If Adam = 450, Rahmad will be 370.
If Adam gives 1/3 of 450 to Rahmad,
Rahmad will get : 370 + 150 = 520.
520 - 450 = 70 (which is 70 more than Adam before the 1/3 is given out).

If Adam gives 1/5 of 450 to Rahmad,
Rahmad will get : 370 + 90 = 460.
460 - 450 = 10 (which is 10 more than Adam).

[tianzhu]

chrisu:

Thanks to all for responding to this post. My daughter came back yesterday evening and told me that the teacher and the Maths HOD agreed to accept both 225 and 450 as answer since the question is ambiguous.


The answer is 225 if comparison is made after the 1/3 and 1/5 is given to Rahmad. The answer will be 450 if the comparison is made before the 1/3 and 1/5 is given to Rahmad.

As for proving of Adam = 450;
If Adam = 450, Rahmad will be 370.
If Adam gives 1/3 of 450 to Rahmad,
Rahmad will get : 370 + 150 = 520.
520 - 450 = 70 (which is 70 more than Adam before the 1/3 is given out).

If Adam gives 1/5 of 450 to Rahmad,
Rahmad will get : 370 + 90 = 460.
460 - 450 = 10 (which is 10 more than Adam).

Hi

Consider this in real life situation.

If I have $450 and I give $150 away, I’ll have $300 left.

I find it difficult to understand the explanation from the school.

Best wishes

[LiteracyICare]

Hi mrswongtuition


Thank you for the link! Appreciate the help there too! I’ll certainly take a look at the resources.

Much gratitude!

[chrisu]

Agreed and that's why it took me one whole night to understand the answer 450 is compared with before the share was given out. Hope that such question will not be out in the PSLE. Too time consuming even to draw the models.


Maybe the school should inform the publisher that there are 2 answers to the question.

tianzhu:

chrisu:

Thanks to all for responding to this post. My daughter came back yesterday evening and told me that the teacher and the Maths HOD agreed to accept both 225 and 450 as answer since the question is ambiguous.

The answer is 225 if comparison is made after the 1/3 and 1/5 is given to Rahmad. The answer will be 450 if the comparison is made before the 1/3 and 1/5 is given to Rahmad.

As for proving of Adam = 450;
If Adam = 450, Rahmad will be 370.
If Adam gives 1/3 of 450 to Rahmad,
Rahmad will get : 370 + 150 = 520.
520 - 450 = 70 (which is 70 more than Adam before the 1/3 is given out).

If Adam gives 1/5 of 450 to Rahmad,
Rahmad will get : 370 + 90 = 460.
460 - 450 = 10 (which is 10 more than Adam).

Hi

Consider this in real life situation.

If I have $450 and I give $150 away, I’ll have $300 left.

I find it difficult to understand the explanation from the school.

Best wishes

[tianzhu]

chrisu:

Agreed and that's why it took me one whole night to understand the answer 450 is compared with before the share was given out. Hope that such question will not be out in the PSLE. Too time consuming even to draw the models.

Hi

The question is why are we comparing with the original amount?

How about this question?

If Mark gives Lenny 14 stickers, he will have the same number of stickers as Lenny. If Lenny gives 10 stickers to Mark, the ratio of the number of stickers Lenny has to that of Mark will be 2: 5. How many stickers does Mark have?

Best wishes

[Hershey]

Hi, can someone please help to solve this 2 maths problem sum using model?


1) Albert and Benny had $282. Benny had $4 more than Albert. Benny spent 1/2 as much as Albert and was left with twice as much as Albert. How much did Benny spent?

2) The ratio of the number of stickers Alex had to the number of stickers Beng Han had was 1:3. After each of them received 25 stickers, the ratio became 3:4. How many stickers did they have altogether at first?

Thank you.

[mrswongtuition]

tianzhu:

chrisu:

Thanks to all for responding to this post. My daughter came back yesterday evening and told me that the teacher and the Maths HOD agreed to accept both 225 and 450 as answer since the question is ambiguous.


The answer is 225 if comparison is made after the 1/3 and 1/5 is given to Rahmad. The answer will be 450 if the comparison is made before the 1/3 and 1/5 is given to Rahmad.

As for proving of Adam = 450;
If Adam = 450, Rahmad will be 370.
If Adam gives 1/3 of 450 to Rahmad,
Rahmad will get : 370 + 150 = 520.
520 - 450 = 70 (which is 70 more than Adam before the 1/3 is given out).

If Adam gives 1/5 of 450 to Rahmad,
Rahmad will get : 370 + 90 = 460.
460 - 450 = 10 (which is 10 more than Adam).

Hi

Consider this in real life situation.

If I have $450 and I give $150 away, I’ll have $300 left.

I find it difficult to understand the explanation from the school.

Best wishes

I agree with Tianzhu.

From language understanding, the question says \"IF.......\" which means that they want us to assume the given scenario, not the original amount.