Q&A - PSLE Math

[jieheng]

Q2)


At first , J had 10u .

After J lost 1u (1/10) to K , J had 9u

Given the ratio of J : K = 3 : 1 .

Since J had 9u , K should have 3u

a)

At first , K had = 3u - 1u = 2u

At first ,the ratio of the number of cards Jimmy had to the number of cards Kelly had = 10 : 2 = 5 : 1 (Ans)


old ratio
J : K Total

3u 1u 4u

After J lost more cards to K

new ratio
J : K Total

4u 7u 11u

Change the ratio of total units to the same number for old ratio and new ratio as the total cards of J and K of old ratio and new ratio should be the same .

Old ratio * 11 and new ratio * 4 , total ratio would be 44

old ratio
J : K Total

33u 11u 44u

new ratio
J : K Total

16u 28u 44u


28u - 16u = 72

12u = 72

1u = 6

Total number of cards = 44u = 44 * 6 = 264

At the end , K had = 28u = 28 * 6 = 168 cards

At first K had = 2/12 * 264 = 44 cards

Number of cards that Kelly won from Jimmy altogether
= 168 - 44
= 124 cards (Ans)

[babyluvv]

Thanks jieheng for helping!!

[jieheng]

Hi babyluvv ,


You are welcome .

[ozora]

I would like to ask any other methods of solving the below questions besides guess and check and algebra.


I have 20 cars and bikes. The number of car wheels are 38 more wheels than the bike. How many cars and bikes are there respectively?

[tianzhu]

ozora:

I would like to ask any other methods of solving the below questions besides guess and check and algebra.


I have 20 cars and bikes. The number of car wheels are 38 more wheels than the bike. How many cars and bikes are there respectively?

Hi

Good Morning.

Yes, we can.

There is always more than one way to arrive at a solution.

We should strive towards a broad based approach to seeking solutions. We should cast our net wide seeking out those with different perspectives on different questions so as to have a vibrant and robust forum for active learning.This’ll benefit our children in the long run.

For your question,the numbers are small, so it’s not too tedious to make calculated guesses using GC if you have to.

A common strategy is to use “Make a Supposition”. A student put up a tabulated list, there are some examples in previous posts.

Another way of making assumption, this time with a slight tweak, is to use the \"pretend pretend\" way.

Assume or pretend that every car and bicycle have 2 wheels at first. Kids have fertile imagination, they like to \"pretend, pretend lah\".I miss this innocent part of a kid's life because my boy is no longer that young already.

Here's the solution.

20*2 ----- 40
40 + 38 ------ 78

2 + 4 ------ 6
78/6 ------ 13

13 cars and 7 bicycles

Best wishes

[pixiedust]

Appreciate any help with the following :


There are 14 pupils in a class.
If each pupil exchanges one sticker with every other one, how many sticker exchanges are made ?

[tianzhu]

pixiedust:

Appreciate any help with the following :


There are 14 pupils in a class.
If each pupil exchanges one sticker with every other one, how many sticker exchanges are made ?

Hi

Draw a diagram to see a pattern.

(13+12+11+10+9+8+7+6+5+4+3+2+1)-------- 91 sticker exchanges

Best wishes

[avell]

Dear all


Pls help me for the following questions:-

Qn (1)
4/5 of John’s money is equal to 3/8 of Sarah’s money. Express Sarah’s money as a ratio of John’s money in it simplest form (draw a model to help you to solve the sum.

Qn (2)
The ratio of boys and girls on a school bus was 2 : 3. When 16 girls alighted from the bus, the ratio of the remaining boys to girls became 6:5. Find the number of children who remained on the bus.

[jieheng]

avell:

Dear all


Pls help me for the following questions:-

Qn (1)
4/5 of John's money is equal to 3/8 of Sarah's money. Express Sarah's money as a ratio of John's money in it simplest form (draw a model to help you to solve the sum.

Hi ,

Q1)

J [ ][ ][ ][ ][ ] 5 units

S [ -][ -][ -][ -][ -][ -][ -][ -] 8 units

To solve the question , need to modify the model , so that the units in Red and Blue are equal

J * 3 and S * 4

J 15 units

S 32 units

Ratio of Sarah's money to John's money = 32 : 15 (Ans)

****************************************************
Faster way to solve this type of question without using the model is to change the numerators of two variables to the same number .

John Sarah
4/5 3/8

Change to

John Sarah
12/15 12/32

Ratio of Sarah's money to John's money = 32 : 15 (Ans)

[jieheng]

avell:

Dear all


Pls help me for the following questions:-

Qn (2)
The ratio of boys and girls on a school bus was 2 : 3. When 16 girls alighted from the bus, the ratio of the remaining boys to girls became 6:5. Find the number of children who remained on the bus.

Old Ratio
B [ ][ ] 2u

G [ ][ ][ ] 3u

New Ratio
B [ ][ ][ ][ ][ ][ ] 6u

G [ ][ ][ ][ ][ ] 5u

Since the number of the boys remained the same throughout the journey ,
modify the old ratio of the boys from 2 units to 6 units

Modified old ratio
B [ ][ ][ ][ ][ ][ ] 6u

G [ ][ ][ ][ ][ ][ ][ ][ ][ ] 9u

Compare the units of the girls of modified old ratio and new ratio ,

4 units = 16
1 unit = 4

Number of children remained on the bus = 11 units (6 units of boys and 5 units of girls) = 11 * 4 = 44 (Ans)