Q&A - PSLE Math

[ozora]

PapayaDad:

Need guide to solve the following questions.

q1. in 20 years time, Tom's age will be 34 years less than twice Joan's age.
If Joan is now 3 times older than Tom, what is Tom's present age?

q2. A is the oldest among three people. When B's age was twice of C's age, A was 30 years old. When A's age was twice of B's age, C was 21 years old. How old was C when A was 62 years old.


the above questions, I have used models to get the answers as follows: Q1 . Tom (1 unit+20years)
Joan( 4unit +20 years) x 2
Tom is 2 years

Sorry, but answer not correct leh.
now Tom is 2, 20 years he is 22
22 + 34 = 56
J = 56/2 = 28
now J is 28 -20 = 8
now Tom = 2
Joan is now 3 times older than Tom...not true
Joan is now 4 times older than Tom.... typo? cuz ur method use 4 units...

3 times older meaning is 4 units.
is a common mistake we assume 3 times older is same as 3 times as..
in fact they are totally different.

[KP2]

Hi,

Could you please help me with this question?

Mr Johnson bought 1.5 times as many toy cars as toy trains. He spent $8456 altogether. A toy train costs $16 more than a toy car. The total cost of the toy trains was $616 less than the total cost of the toy cars. Find the cost of the toy car.

[KP2]

Hi,

Could you please help me with this question?

Mr Johnson bought 1.5 times as many toy cars as toy trains. He spent $8456 altogether. A toy train costs $16 more than a toy car. The total cost of the toy trains was $616 less than the total cost of the toy cars. Find the cost of the toy car.

[MathIzzzFun]

KP2:

Hi,

Could you please help me with this question?

Mr Johnson bought 1.5 times as many toy cars as toy trains. He spent $8456 altogether. A toy train costs $16 more than a toy car. The total cost of the toy trains was $616 less than the total cost of the toy cars. Find the cost of the toy car.

total cost for the trains = $(8456-616)/2 = $ 3920
total cost for the toy cars = $8456 - $3920 = $4536

number of trains --> 2 units, cost of trains/unit --> $3920/2 = $1960
number of toy cars --> 3 units, cost of toy cars/unit --> $4536/3 = $1512

Number of cars/toy in 1 unit = ($1960-$1512)/$16 = 28

cost of 1 train --> $ 2960/28 = $70
cost of 1 toy car --> $1512/28 = $54

cheers.

[ozora]

Need guide in the following double if questions.

Q1. A team of students calculated their average score for their tests.
If anyone of them scored 5 points less, their average score would be 87.
If anyone of them scored 13 more points, their average score would be 90.
How many students are there?

Q2. A baker made some cookies.
If he packs a vanilla cookie with a choco cookie, there will be 60 choco cookies left.
If he packs every 2 vanilla cookies with 3 choco cookies, there will be 50 vanilla cookies left.
how many cookies did he make?
thanks

[tianzhu]

YumYum:

Hi, can someone pls help with these Qns:


1) Mary bought some red marbles and have half to Noel.
Noel bought some blue marbles and gave half to Mary.
Mary lost 16 red marbles and Noel lost 55 blue marbles.
The ratio of Mary's red marbles to blue marbles became 18:55 and the ratio of Noel's red marbles to blue marbles became 7:20.
How many red marbles did Mary buy?

Hi

Please check with your source.

We could not get nice whole number as the answer.

Perhaps, it should be read as 18:85

The solution is based on the revised ratio of 18:85

Hope this helps

Best wishes

http://farm8.staticflickr.com/7456/8722620110_27aa90062c_z.jpg\">

[KP2]

:thankyou: MathIzzzFun

[fullhope]

Thanks Tianzhu for the answer.

[fullhope]

Thanks Tianzhu for the answer.

[YumYum]

Tianzhu, thks for yr help the Qn on the marbles, the ratio is indeed 18:85. My mistake in typing it out. Thanks :rahrah: