Q&A - PSLE Math

[Brenda10]

tianzhu:

Hi


Some interesting questions from onsponge.
3)Ben and Marcus received some money from their mother. Marcus would have $64 more than Ben if Ben gave 2/5 of his share to Marcus. Marcus would have $144 more than Ben if Ben gave 2/3 of his share to Marcus. How much money did Ben receive from his mother? (Singapore Chinese Girls' School P6 2010 SA1 Maths Q13)

Best wishes

Hi Tianzhu

DD working:

3/5 = 6/15
2/3 = 10/15

10- 6= 4
144 - 64 = 80
80 / 4 = 20
15 x 20 = 300*

*This answer is different with the answer key: 150

We then checked the onsponge forum and realize that instead of 10 - 6 =4 , it should be 10 + 10 = 20, 6 + 6 = 12** and resulted 20 - 12 = 8

As such, it will become :
80/ 8 = 10
15 * 10 = 150

**DD cannot understand this particular step and appreciate your kind help.

Thank you

[tianzhu]

Hi Brenda10


It’s good to draw a model for this question.

You have a good start; you’ve worked out the common multiple for 3 and 5 which is 15.

To begin, Ben has 15 units.

In the first case, Ben gave 6 units to Marcus,leaving a remainder of 9 units.

In the second case, Ben gave 10 units to Marcus, leaving a remainder of 5 units.

The difference between the first and second case is 8 units(take away 4 units for Ben and add 4 units to Marcus) and their difference is 80.
This gives 1 unit equal to 10.

I remember drawing out the MD for a similar type of question some months ago; I’ll try to find it. If I can’t find it, I’ll draw the MD for this question and give to you early next week.

Best wishes

[Brenda10]

tianzhu:

Hi Brenda10


It’s good to draw a model for this question.

You have a good start; you’ve worked out the common multiple for 3 and 5 which is 15.

To begin, Ben has 15 units.

In the first case, Ben gave 6 units to Marcus,leaving a remainder of 9 units.

In the second case, Ben gave 10 units to Marcus, leaving a remainder of 5 units.

The difference between the first and second case is 8 units(take away 4 units for Ben and add 4 units to Marcus) and their difference is 80.
This gives 1 unit equal to 10.

I remember drawing out the MD for a similar type of question some months ago; I’ll try to find it. If I can’t find it, I’ll draw the MD for this question and give to you early next week.

Best wishes

Hi Tianzhu

Thank you for your explanation and we wish you a nice weekend.

[Suz855]

Hi,


Looking for better way to solve the following question, your kind input will be most appreciated.

Question
Mr Sum had 120 ovens. He sold 40% of the oven at their usual price and half of the remainder at a discount of 15% of the usual price. He sold the rest of the ovens at their cost price of $380 each. He earned $1878. What was the price of each oven after the discount?

Thanks a million
:idea:

[tianzhu]

Brenda10:

Thank you for your explanation and we wish you a nice weekend.

Hi Brenda10

Good Morning

Great, you got it.

This is a double if question where you need to compare two cases or scenarios. The if is used to introduce some event that may happen but in reality nothing truly or ever happened.

Once you are able to break down the question and see that 8 units is equal to 80, the rest of the calculations is a breeze.

I believe you don’t need the MD from me now.

Enjoy your weekend, too.

[Brenda10]

tianzhu:

Brenda10:

Thank you for your explanation and we wish you a nice weekend.

Hi Brenda10

Good Morning

Great, you got it.

This is a double if question where you need to compare two cases or scenarios. The if is used to introduce some event that may happen but in reality nothing truly or ever happened.

Once you are able to that the break down the question and see that 8 units is equal to 80, the rest of the calculations is a breeze.

I believe you don’t need the MD from me now.

Enjoy your weekend, too.

Good morning Tianzhu

Yes. You're right that now dd can understand why is 8 units and I believe if there are similar questions in other papers she should be able to handle.

Thank you.

[tianzhu]

Suz855:

Mr Sum had 120 ovens. He sold 40% of the oven at their usual price and half of the remainder at a discount of 15% of the usual price. He sold the rest of the ovens at their cost price of $380 each. He earned $1878. What was the price of each oven after the discount?

Hi Suz855

Good Morning

You may use Number*Value method to solve this question. A diagram may help one to see the problem better.

I believe this is a paper 2 question and you're allowed to use the calculator.

First, work out the number of ovens as follows,

Usual price (UP) ----- 48
85% of UP ----- 36
Cost price ($380) ----- 36

Cost price of 120 ovens ----- (120*380) ----- 45600
He earned $1878, meaning the selling price of 120 ovens is $47478

To avoid working with decimals, I’d use 100u to represent the UP and 85u to show the discounted price.

Therefore the selling prices are as follows

48*100u ----- 4800u
36*85u ----- 3060u
36*380 ----- 13680

They add up to $47478, you’ll get 1u equals to 4.3

3060*4.3/36 ----- 365.50

The discounted price of oven ----- $365.50

Best wishes

[tianzhu]

Brenda10:

Good morning Tianzhu

Yes. You're right that now dd can understand why is 8 units and I believe if there are similar questions in other papers she should be able to handle.

Thank you.

Hi Brenda10

You're welcome.

Best wishes

[Suz855]

Hi Tianzhu,


Yes calculator can be used & thanks for the clear & great solution ....have a great wk ahead

cheers

[Tang]

Suz855:

Hi,


Looking for better way to solve the following question, your kind input will be most appreciated.

Question
Mr Sum had 120 ovens. He sold 40% of the oven at their usual price and half of the remainder at a discount of 15% of the usual price. He sold the rest of the ovens at their cost price of $380 each. He earned $1878. What was the price of each oven after the discount?

Thanks a million
:idea:

100% --> 120 ovens

10% --> 10/100 x 120 = 12

40% --> 4 x 12 = 48 ovens

1/2 x 60% = 30% --> 3 x 12 = 36 ovens

48 + 36 = 84

48 x 1 u + 36 x 0.85 u --> 1878 + 84 x 380 = 33798

1 u --> 33798/78.6 = 430

0.85 u --> 0.85 x 430 = $365.50

The price of oven after discount was $365.50.