Q&A - P3 Math

[AgonyMum]

Thanks very much, php

I know my mistake now...I assumed that the total amount of $26 remains unchanged.
I have understood your solution.
Thanks!

[CoffeeCat]

HAPPYH:

Michaelia0816:

Not possible, to use three, but after comparing two and found one of it, use it for another to compare.

Could you please help me solve the following problem using the above method? Thank you in advance.

Si Rong had 8 50 cent-coins, 20 cent coins and 10 cent coins that add upto $2. How many 50 cent coins does she have?

Yep primary school students are expected to do this using guess-and-check. Notice that there is only 2 equations and 3 variables, so that standard simultaneous equation method can't be used. However such question has appeared before in SMOPS, and an algebraic method do exists.

[lydia_chin]

Hi, pls assist with this question:


There are an equal number of pupils from Class A and Class B at the football field. After a while, half of the pupils from Class A and 42 pupils from Class B left the field and there were 12 more pupils from Class A than Class B remaining at the field.

How many pupils were there at the field at first?

Thanks!

[php]

lydia_chin:

Hi, pls assist with this question:


There are an equal number of pupils from Class A and Class B at the football field. After a while, half of the pupils from Class A and 42 pupils from Class B left the field and there were 12 more pupils from Class A than Class B remaining at the field.

How many pupils were there at the field at first?

Thanks!

A <-----1 unit-------><---1 unit (left)-->

B <--------><----------42 left ---------->


1 unit --> 42 - 12 = 30
4 units --> 30 x 4 = 120

Ans : 120

[BigDevil]

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[lydia_chin]

Thanks php & Bigdevil!

[cathycho]

What is the fastest way to do this sum?


Find the sum of 18+20+22+…+36+38+40

[CoffeeCat]

cathycho:

What is the fastest way to do this sum?


Find the sum of 18+20+22+........+36+38+40

Hi, notice that there is a pattern in the numbers, which led to the insight that 18+ 40 = 20 + 38 = 22 + 36, i.e. one can distribute the numbers evenly.
so the average will be (18+40)/2 = 29
And there are 12 such terms, total will be 12*29 = 348

The standard formula is total = average * no. of terms

[cathycho]

Thks, CoffeeCat.

[lydia_chin]

Can someone help with this sum?


Susan had twice as many stamps as Lisa. After Susan gave away 120 stamps to her brother and Lisa gave away 48 stamps to her friend, they had an equal number of stamps.

How many stamps does Susan had at first?