Q&A - PSLE Math

[MathIzzzFun]

Fat Mama:

Hi,


Need help in this qn :

I have some red and blue ribbons in a bottle.
If I add 20 red ribbons, 60% of my ribbons are blue.
If I add another 60 blue ribbons, 75% of my ribbons are blue.
How many ribbons do I have in the bottle?

Tks

Hi

IF 20 red ribbons added, Red: Blue = 2 units : 3 units
(At first, number of Red: Blue = 2 units - 20 : 3 units)

IF another 60 blue ribbons added,
Red : Blue
= 2 units : 3 units + 60
= 1 : 3

--> 2 units = 1 unit + 20 --> 1 unit = 20

Total number of ribbons = 5 units - 20 = 100 - 20 = 80

cheers.

[Fat Mama]

Hi MathIzzzFun


Tks for ur soln. Answer given was 180 ribbons.

Then I use ur ans to substitute in.
At first in the bottle is 20 red and 60 blue.
Add 20 red means 40 red and 60 blue. Correct
Add 60 blue means 20 red and 120 blue. Ratio is 1 : 6 Wrong

I dun quite understand the sentence "IF another 60 blue ribbons added, ", does it means that 60 blue ribbons is added on top of the 20 red ribbons? Or we have to solve it separately?

Tks

[MathIzzzFun]

Fat Mama:

Hi MathIzzzFun


Tks for ur soln. Answer given was 180 ribbons.

Then I use ur ans to substitute in.
At first in the bottle is 20 red and 60 blue.
Add 20 red means 40 red and 60 blue. Correct
Add 60 blue means 20 red and 120 blue. Ratio is 1 : 6 Wrong

I dun quite understand the sentence \"IF another 60 blue ribbons added, \", does it means that 60 blue ribbons is added on top of the 20 red ribbons? Or we have to solve it separately?

Tks

Hi

The question says : \" If 20 red ribbons is added..... If I add ANOTHER 60 blue ribbons... '

This means there are 2 conditions - first, 20 red ribbons is added, 2nd, ANOTHER 60 blue ribbons is added (with the 20 additional red still in the bottle).

So, we start with 20 red, 60 blue. Add 20 red --> 40 red, 60 blue --> ratio of red : blue = 2 :3 --> add another 60 blue --> 40 red, 120 blue --> ratio of red: blue = 1 : 3 ie blue ribbons make 3/4 of the ribbons.

To get 180 ribbons in bottle, the question has to be amended as follows:
I have some red and blue ribbons in a bottle.
If I add 20 red ribbons, 60% of my ribbons are blue.
If I add 60 blue ribbons, 75% of my ribbons are blue.
How many ribbons do I have in the bottle?

cheers.

[tianzhu]

Hi Fat Mama


Sometimes, the words used by the question setter may be open to interpretations. The answers may vary in accordance to the interpretation of the questions by the students.

Compare your question to these past year questions.

Q1) Mrs Lim bought some bowls and plates. If she buys another 5 bowls, there are 60% as many bowls as plates. If she buys another 9 plates, there will be thrice as many plates as bowls. How many bowls did she buy? (CHS P5 SA2 2009)

Q2) Susan has some vanilla and chocolate sweets in her bag. If she adds 20 vanilla sweets into the bag, the percentage of vanilla sweets in the bag becomes 40%. If she adds 30 chocolate sweets, there will be 70% of chocolate sweets in the bag. How many vanilla and chocolate sweets does she have? (P6 2010 SA2 River Valley P2 Q18)

For Q1, another is used in both conditions. For Q2, another is omitted.

How would you interpret and solve Q1?

The interesting point is, “Does the word another make any difference in meaning?

For example,

If you add 20 eggs
If you add another 20 eggs
If you add 20 more eggs

Do these phrases mean the same thing?

Best wishes

[Fat Mama]

Hi MathIzzzFun and Tianzhu


Thank you v much for yr explanation.

Tianzhu,

For Q1, I’ll interpret the 2 conditions separately and not 5+9 bowls. Am i correct?

Thanks

[tianzhu]

Fat Mama:

For Q1, I'll interpret the 2 conditions separately and not 5+9 bowls. Am i correct?

Hi

I am given the understanding that you interpreted the two conditions separately for Q1. How does it compare to your interpretation for your question?

The “if” in a statement signifies the event didn’t really happen.

For questions on “double if”, students work on the assumption that those scenarios didn’t happen. The two conditions are also independent or exclusive as in Q2.

Q2) Susan has some vanilla and chocolate sweets in her bag. If she adds 20 vanilla sweets into the bag, the percentage of vanilla sweets in the bag becomes 40%. If she adds 30 chocolate sweets, there will be 70% of chocolate sweets in the bag. How many vanilla and chocolate sweets does she have? (P6 2010 SA2 River Valley P2 Q18)

However, in your question, in the second condition, the additional word another is added. What does the question setter have in mind at the moment when crafting this question?

Does it mean that first we add 20 ribbons and then we add another 60 ribbons to it?

If this is so, then we are lumping the two “if” conditions into one.

Having said that, could we use the same perspective to solve Q1?

Q1) Mrs Lim bought some bowls and plates. If she buys another 5 bowls, there are 60% as many bowls as plates. If she buys another 9 plates, there will be thrice as many plates as bowls. How many bowls did she buy? (CHS P5 SA2 2009) ----- (answer is 13)

Have some thoughts over these phrases, do they mean the same thing?

If you add 20 eggs
If you add another 20 eggs
If you add 20 more eggs

I think you need to work out the solution to Q1, and then compare it to your solution to your question to appreciate how one’s interpretation affects the answers.

Where is your question from? If it is from assessment books, I suggest you write to the publisher for clarification.

Best wishes

[Fat Mama]

My qn is from Nan Hua, P6 CA1 2011 Qn 7.

[fightingmom]

Please help:


Mrs Tan bought some fruits. 1/9 of the fruits were pears, 3/4 of the remaining fruits were oranges and the rest were mangoes. The prices of the fruits were as shown below:

Pears : $0.60 each
Oranges : $0.45 each
Mangoes : $1.50 each

She spent $19.80 on the pears and mangoes. How much did she spend on the mangoes?

[Ichigokun]

Oh my god. I just realised after going to Secondary School I forgot how to do Primary School math!! WAHAHAHA. Forgotten everything during the hols after PSLE.

[MathIzzzFun]

fightingmom:

Please help:


Mrs Tan bought some fruits. 1/9 of the fruits were pears, 3/4 of the remaining fruits were oranges and the rest were mangoes. The prices of the fruits were as shown below:

Pears : $0.60 each
Oranges : $0.45 each
Mangoes : $1.50 each

She spent $19.80 on the pears and mangoes. How much did she spend on the mangoes?

Hi

I think the $19.80 is spent on pears and oranges, otherwise Mrs Tan would have bought 1/2 a pear

1) $ 19.80 spent on pears and mangoes

number of pears, oranges and mangoes --> 1 : 6 : 2

1 pear + 2 mangoes --> $ 0.60 + $ 1.50 x 2 = $ 3.60
$ 19.80 / $ 3.60 = 5.5
number of pears --> 5.5
number of oranges --> 6 x 5.5 = 33
number of mangoes --> 5.5 x 2 = 11
amount spent on mangoes = 11 x $ 1.50 = $ 16.50

2) $ 19.80 spent on pears and oranges

1 pear + 6 oranges --> $ 0.60 + $ 0.45 x 6 = $ 3.30
$ 19.80 / $ 3.30 = 6
number of pears --> 6
number of oranges --> 6 x 6 = 36
number of mangoes --> 2 x 6 = 12
amount spent on mangoes = 12 x $ 1.50 = $ 18

cheers.