Q&A - P3 Math

[Champion]

tianzhu:

Champion:

Hi Tianzhu & all parents,

Need your help with the following questions that DD1 came home with worksheet from school.

(1) The sum of two numbers is 7500. The greater number is twice that of the smaller number. What are the 2 numbers?

(2) Kenneth has 9 coins that add up to $2.70. Some of them are 50-cent coins and the rest are 20-cent coins. How many 50-cent coins does he have?

(3) John and Samy shared 72 sweets. John received twice as many sweets as Samy. How many sweets did John receive?

Hi Champion
I take them as P3 questions.

Q1 and Q3 are pretty similar.
You may use MD to solve them.

Big number ------ 2 units (2 rectangular blocks)
Small number -----1 unit (1 rectangular block)

3 units ------7500
1 unit ------ 2500

The two numbers are 5000 and 2500.

John ------ 2 units
Samy -----1 unit

3 units ------ 72
1 unit ------ 24

John ------ 2 units ------- 48

For Q2, a P3 student may make calculated guesses using a strategy called GC. The numbers are small and it’s not too tedious to arrive at the solution.

Or, he/she may use a heuristics known as “Draw a diagram”

In this solution, I’ll share how to solve by “Make a Supposition”. This strategy is more efficient and is used commonly in upper primary level.

Assume all were 20 cents coins.

9*20 ------ 180
270 – 180 ------90

Difference between 50 cents coin and 20 cent coin -------- 30

90/30 -------3

Hence 3 50 cents coins

Best wishes

Hi Tianzhu,
Thanks so much for your detailed explanation; appreciates :thankyou:

Yes, the above questions are meant for P3 but was rather stunned when I looked at the worksheet when DD brought back today. Reason being that she has not being taught Division and the relief teacher solved Q1 using division: 7500/3 = 2500. Then 2500x2=5000. Big number 5000 and small number 2500.

So I decided to post the questions to seek help from you and other parents. After seeing your analysis, I grasp more concepts lioa

[Nebbermind]

are the p3 taught division like the way we used to do…working with the ‘biggest’ number, get the remainder, repeat until the smallest number?


I don’t remember my boy having to go thru that…and eventually they all use calculators.

[tianzhu]

Champion:

Hi Tianzhu,
Thanks so much for your detailed explanation; appreciates :thankyou:

Hi Champion

You're welcome.

Best wishes

[deep]

Before a game, Benson had 3/5 as many marbles as Sharul. During the game, Sharul lost 63 marbles to Benson, after which Benson had twice as many marbles as Sharul. How many marbles did Benson have at first?

[tianzhu]

deep:

Before a game, Benson had 3/5 as many marbles as Sharul. During the game, Sharul lost 63 marbles to Benson, after which Benson had twice as many marbles as Sharul. How many marbles did Benson have at first?

Hi

You may use the Units Method.

At first
Benson ----- 3 units ------- 9 units
Sharul ------ 5 units ------- 15 units
Total ------- 8 units -------- 24 units

In the end.
Benson ----- 2 units -------- 16 units
Sharul ----- 1 unit ------- 8 units
Total ----- 3 units ------- 24 units

The total number of marbles before and after the transfer remains the same. Make the total number of units before and after the same.A common multiple of 3 and 8 is 24.

Difference in units ------ 7 units
7 units ------63
1 unit ------- 9

Benson ------ 9 units ------- 81 marbles

Best wishes

[deep]

Why is it become 9 and 15? cant understand that…

[tianzhu]

deep:

Why is it become 9 and 15? cant understand that..

Hi

The total number of marbles before and after the transfer remains the same. Make the total number of units before and after the same.A common multiple of 3 and 8 is 24.

At first
Benson ----- 3 units ------- 9 units (3*3)
Sharul ------ 5 units ------- 15 units (5*3)
Total ------- 8 units -------- 24 units (8*3)

Do the same for \"In the end\" units.This time multiply each row by 8

In the end.
Benson ----- 2 units -------- 16 units
Sharul ----- 1 unit ------- 8 units
Total ----- 3 units ------- 24 units

Best wishes

[shurley197323]

Pls help. MRS CHENG USED 4/5KG OF 2KG OF SUGAR TO MIX WITH SOME FLOUR. THE AMOUNT OF FLOUR SHE USED IS 1/10KG LESS THAN THE AMOUNT OF SUGAR. WHAT WAS THE MASS OF THE MIXTURE.?

[blessedami]

shurley197323:

Pls help. MRS CHENG USED 4/5KG OF 2KG OF SUGAR TO MIX WITH SOME FLOUR. THE AMOUNT OF FLOUR SHE USED IS 1/10KG LESS THAN THE AMOUNT OF SUGAR. WHAT WAS THE MASS OF THE MIXTURE.?

Hi

Do you mean 4/5 of 2kg of sugar?? :?

If so, then 4/5 of 2kg would be 4/5 of 2000g which is 1600g

Then, since he used 100g (1/10 kg is 100g) less flour, he used 1500g of flour.

So, the total would be 1600g + 1500g = 3100g = 3kg 100g

Not really sure though....

[shurley197323]

Yes.Thanks blessedami. The answer is the same. 3kg100g