Q&A - PSLE Math

[jesschan]

tianzhu:

jesschan:

This is a P5 maths question - not sure is this the correct place to post.


A man spent $1119 on a diamond using $50, $5 and $2 notes. The total number of notes used is 45. How many $50, $5 and $2 notes did he use?

I know how to solve it using Guess and Check - just wondering if there is a quicker method?

Hi jesschan

I did a quick check, is the answer, 20 pieces of $50, 23 pieces of $5 and 2 pieces of $2?

I’ll try to consolidate my thoughts at a later time to present the solution in more details if the answer is correct.


Yes, it's correct.

Best wishes

[shurley197323]

cwc:

Let R be the number of rows.


21R = 16 (R+7) + 8
= 16R + 120
5R = 120
R = 24

So 21 * 24 = 504

Correct right?!?!

Hi. Thanks cwc. But why 5R = 120?
Why must 120 / 5 ?
How to explain? Thanks

[tianzhu]

shurley197323:

In a school hall, a certai no of students can be arranged such that there are exactly 21 students per row. If the same no of students is arranged in rows of 16 students each. there will be 7 more rows and 8 students left over. How many students are there altogether?

Hi

This question looks tricky at first glance, however, it can be rearranged into a familiar question.

Restate this question in another way, Try to view it from another angle and perspective.

In a school hall, a certain no of students can be arranged such that there are exactly 21 students per row. If the same no of students is arranged in rows of 16 students each, there will be 120 students left over. How many students are there altogether?

7 more rows of 16 students plus 8 will give 120.

Does it now look familiar to this question?

Mr Tan had some charity tickets. If he sends 4 tickets each to some companies, he will need 20 more tickets. However, if he sends 3 tickets each to the same companies, he will have a remainder of 50 tickets. How many tickets does he have?

Now the solution to your question

Difference in number of students per row ------ 21 - 16 ----- 5
Gap -------- 120
Number of rows --------120/5 ------24

Number of students --------- 24*21 ------- 504

Best wishes

[mvmir26]

Thank you very much for your help. Tianzhu.





quote=\"tianzhu\"]

mvmir26:

Anyone can help me with below questions:-
Mr Tan had a total of 350 ducks and chickens in his farm. After selling some ducks and chickens he had 100 of them left. The ratio of the number of chickens sold to the number of chickens left was 4:1. The number of ducks sold to the number of ducks left was 3:2. How many chickens were sold by Mr Tan?

Hi

This is a question on simultaneous concepts.

If a student is familiar with simultaneous equations, he/she may use it.

If not,solve it using the ‘Alphabet Method” or solve the equations pictorially.

Let’s begin using the “Alphabet Method”

Number of chickens sold ------ 4C
Number of chickens left ------ 1C

Number of ducks sold ------ 3D
Number of ducks left ------2D

5C + 5D ------350
1C + 1D ------70

1C + 2D ------ 100
1D -------30
1C ------40

Number of chicken sold --------4*40 ------160

Best wishes[/quote]

[shurley197323]

Thanks Tianzhu and cwc.

[ozora]

tianzhu:

Hi


For Q1, a student should recognize that the amount of money stays the same after the transfer.

As for Q2, “Systematic Listing” is commonly used by students.
There are multiple answers to your question.
107 is one of them. I think there are three more answers, 119, 131 and 143.

Hope this helps.

Best wishes.

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thanks i got the answer for question 2 is 107 but the given answer is 131. I was puzzled where did i go wrong.
I did the listing method.

[tianzhu]

shurley197323:

Thanks Tianzhu and cwc.

Hi shurley197323

Good Morning.

You're welcome.

Best wishes

[tianzhu]

ozora:

thanks i got the answer for question 2 is 107 but the given answer is 131. I was puzzled where did i go wrong.

I did the listing method.

Hi ozora

Good Morning.

You're welcome.

Best wishes

[tianzhu]

mvmir26:

Thank you very much for your help. Tianzhu.

Hi mvmir26

Good Morning.

You're welcome.

Best wishes

[tianzhu]

Hi jesschan


Good Morning.

I hope I’ve not kept you waiting for too long.

For your question, a P5 student should be able to use logical reasoning to breakdown the problem.

You are given the notes in denominations of $50, $5 and $2.

To add up to $1119, you need the value of $2 notes to end up in $4, $14,$24 … that is number ending with 4 because we are adding to multiples of $5 notes.

Using knowledge of number bonds, we have 1119 ----- 1100 + 15 + 4

Once a student is able to breakdown the question into this pattern, the rest of the calculations come into place. The next step is to allocate the right denominations of notes to add up to $1119.

An alternative solution is to use “Assumption Method”.

1119 ------ 1110 + 5 + 4

5 + 4 ----- use 1 number of $5 note and 2 number of $2 notes

Hence , the remaining 42 number of notes with a total value of $1110 consists of $50 and $5 notes.

Now, use “Assumption Method” to find the number of $50 notes and $5 notes.

Hope this helps.

Best wishes

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