Q&A - P3 Math

[whywhy]

Tin A contains some 20-cents coins and Tin B contains some 50-cents coins.

There are 9 more coins in Tin A than in Tin B.
The amount of money in Tin A is $2.70 less than that in Tin B.
How many 50-cents coins are there in Tin B ?

Is guess and check the only method to solve this Question???

[tianzhu]

whywhy:

Tin A contains some 20-cents coins and Tin B contains some 50-cents coins.

There are 9 more coins in Tin A than in Tin B.
The amount of money in Tin A is $2.70 less than that in Tin B.
How many 50-cents coins are there in Tin B ?

Is guess and check the only method to solve this Question???

Hi

Suppose or pretend that you remove 9 20 cents coins from Tin A.

9*20 ---- 180

Now Tin A has (270+180) or 450 cents less than Tin B

Difference in value between a 50 cents coin and 20 cents coin ------ 30 cents.

450/30 ------ 15

There are 15 50 cents coins in Tin B.

Best wishes

[pixiedust]

Is this P4/P5 question ?


…num of coins…*…value…Total amt of money
Tin A…U+9…20cents…20U+180
Tin B…U…50cents…50U
(…for alignment purpose)

50U = 20U + 180 + 270 = 20U + 450
30U = 450
U=15

Ans: There are 15 50-cents coins in Tin B.

---------------------------------------------------
check :
Tin B: 15 coins -> 15 x 50cents = $7.50
Tin A: 24 coins -> 24 x 20cents = $4.80
$7.50-$4.80=$2.70, checked

[pixiedust]

tianzh’s method is faster and more elegant !

[atutor2001]

1 method uses heuristic (in the past we remembered this approach as "making it equal and then working in pairs) while the other is pure mathematical approach.

I would pick the latter for the sake of future development to tackle complex problem.

[ET-PH]

atutor2001:

1 method uses heuristic (in the past we remembered this approach as \"making it equal and then working in pairs) while the other is pure mathematical approach.

I would pick the latter for the sake of future development to tackle complex problem.

The latter method uses the algebra concept, ie. let U be the number of 50 cents coins, just wonder if this is acceptable in school.

[whywhy]

Thank u all. This is a p4 question. I. will show my boy and see which method he can understand better. what abt your kids ? Heuristic or algebra method? Let’s poll n see.

[atutor2001]

ET-PH:

The latter method uses the algebra concept, ie. let U be the number of 50 cents coins, just wonder if this is acceptable in school.

Most top schools accept such method. My kids used such method more than 10 years ago (it was actually taught by one of their teachers who later became a math teacher for GEP). Yes there were complaints from some teachers but I ignore them. However, it is important to train the kids to start the question with \"Let ..... be ..U\" so that they have a good base for sec math.

The important thing is that if they don't get use to such mathematical modelling approach, it will be a nightmare solving complex problem sum. Based on what I see, the current 5 mark problems usually involve 3 unknowns. To solve with model is really tedious. Kids with know how on algebra and simultaneous can tackle them easily.

[atutor2001]

whywhy:

Thank u all. This is a p4 question. I. will show my boy and see which method he can understand better. what abt your kids ? Heuristic or algebra method? Let's poll n see.

No need to poll. More than 80% will go for heuristic. There is a strong belief that by understanding the solution heuristically, the children will go on to develop skills to tackle problem sum better. Unfortunately it is not very true. Otherwise mathematical method would not have been invented.

Cheers

[smartmummy]

Hi All!

I have a Qn.
A piece of ropeis 5m long.It is cut into two pieces.The first piece is longer by 20cm.What is the length of the second piece?
I did using model the answer was 260.
I did use Guess and check method answer was 270.
Are that my two answers correct?

For problem sums we need to draw models and number equations then sentence???