Q&A - P3 Math

[Michaelia0816]

The marks are found in the workings and a mark for the final answer correct.

[AgonyMum]

Can someone help confirm if the corret answer is $12 or $10? I worked through it a few times and my answer is $12. The answer sheet states $10 though…

Please show mw how to derive the correct answer.Thanks very much!

Qn. Jenny and May had $26 altogether at first. After spending $4, Jenny received $5 from May. They have the same amount of money after that.How much did Jenny have at first?

[php]

AgonyMum:

Can someone help confirm if the corret answer is $12 or $10? I worked through it a few times and my answer is $12. The answer sheet states $10 though....

Please show mw how to derive the correct answer.Thanks very much!

Qn. Jenny and May had $26 altogether at first. After spending $4, Jenny received $5 from May. They have the same amount of money after that.How much did Jenny have at first?

Before --> Total = $26

Jenny --> -$4 + $5
May --> -$5

After --> Total = $22
Jenny -> 1 unit
May -> 1 unit

2 units --> $22
1 unit --> $11

Working Backward

Jenny --> $11 + $4 - $5 = $10

Ans : $10

[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