Q&A - PSLE Math

[autolycus]

Rockdiva:

so can i say that the p6 qns are mostly on assumptions and logic thinking and no distinct formula to work it out?

Yes, because for most schools at P6 nowadays, algebra isn't taught as the main method of solving problems. That's why my solution doesn't use algebra. And that is why 'distinct formulae' are not normally the way to go...

[shurley197323]

There are 1000 desks in an examination hall.Mages numbers all the desk in running order starting from 1. What is the total number of digits she writes? Besides doing manually listing out 1 by 1. Is there any shortcuts or formula for this ? Pls help. Thank you.

[tianzhu]

shurley197323:

There are 1000 desks in an examination hall.Mages numbers all the desk in running order starting from 1. What is the total number of digits she writes?

Hi

Hope this helps.

1 to 9 ------ 9 digits
10 to 99 ------ 180 digits
100 to 999 ------ 2700 digits
1000 ------ 4 digits

Total number of digits ------ (9+180+2700+4) ------- 2893

Best wishes

[shurley197323]

Thanks for your help. Tianzhu

[tianzhu]

shurley197323:

Thanks for your help. Tianzhu

Hi

You're welcome.

Best wishes

[Hifive]

Hi


I need help with this question:

Peter, Sally, Kelly and Devi saved $4050 altogether in January. In February, Devi saved 20% more than in January, Kelly spent 25% of her money, Sally saved another $200 and Peter spent $500. All of them had the same amount of money at the end of February. How much did Devi save in January?

Answer given is $750.

Thanks in advance.

[tianzhu]

Hifive:

Peter, Sally, Kelly and Devi saved $4050 altogether in January. In February, Devi saved 20% more than in January, Kelly spent 25% of her money, Sally saved another $200 and Peter spent $500. All of them had the same amount of money at the end of February. How much did Devi save in January?

Answer given is $750.

Hi

You may wish to use MD.
Start from the end.

Devi --------18 units
Kelly -------- 18 units
Sally --------- 18 units
Peter --------- 18 units

At first
Devi --------15 units
Kelly -------- 24 units
Sally --------- 18 units -200
Peter --------- 18 units +500

At first, they had $4050

75 units ------4050+200-500 -------3750
1 unit ------ 50

15 units ------750 (Devi’s saving in January)

Best wishes

[Hifive]

tianzhu:

You may wish to use MD.
Start from the end.

Devi --------18 units
Kelly -------- 18 units
Sally --------- 18 units
Peter --------- 18 units

Hi tianzhu

Thank you for the solution.
Sorry I can't figure out, can you pls explain why you use 18 units in this case?

Thanks & Regards

[tianzhu]

Hifive:

can you pls explain why you use 18 units in this case?

Hi Hifive

Good Morning.

I’ll explain how to arrive at 18 units.

In February, Devi saved 20% more than in January.

For Devi

In Jan, she had 5 units.
In Feb, she saved 20% more than in Jan, therefore she had 6 units.

In February, Kelly spent 25% of her money.

Divide the bar in the MD into 4 parts.
In Feb, she had 3 parts left, after spending 1 part (25%)
Therefore in Jan, she had 4 parts.

All of them had the same amount of money at the end of February.

If you use MD to solve this question.
Start with a big box (bar) for Devi.
Divide into 6 smaller units.

Kelly had 3 parts left.

Apply the equal concept; a common multiple of 3 and 6 is 18.

Trying drawing out the MD, if you need more information, please let me know. Due to time constraints, I’ll skip drawing the MD this time.

Another alternative to solve this question is to use the Units method.

Hope this helps.

Best wishes.

[Hifive]

Hi tianzhu


Thanks for your explanation, now I can understand the steps better.

Have a nice day!