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教育王國 › 討論區 › 小學雜談 › P4 Maths - Please help. Thanks!
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P4 Maths - Please help. Thanks! [複製鏈接]

hhmami

Rank: 3Rank: 3


105
1#
發表於 05-11-10 22:29 |只看該作者

P4 Maths - Please help. Thanks!

Please help for the Maths question below:

The average of 4 numbers is 60.  The average of 5 numbers is 80.  What is the fifth number?

Thanks a lot.

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DSS

Rank: 5Rank: 5


1095
2#
發表於 05-11-10 22:31 |只看該作者

Re: P4 Maths - Please help. Thanks!

the difference is the 5th number:

5 x 80 - 4 x 60 =

160

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Yukyuk

Rank: 5Rank: 5

醒目開學勳章


4119
3#
發表於 05-11-10 22:36 |只看該作者

Re: P4 Maths - Please help. Thanks!

Let a be 1st,
b be 2nd, c be 3rd, d be 4th and e be 5th. number.

a+b+c+d = 60 x 4 = 240

a+b+c+d +e = 80x5 = 400

So, 240 + e = 400

e = 160




hhmami 寫道:
Please help for the Maths question below:

The average of 4 numbers is 60.  The average of 5 numbers is 80.  What is the fifth number?

Thanks a lot.

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daisychan

Rank: 5Rank: 5


3465
4#
發表於 05-11-10 22:57 |只看該作者

Re: P4 Maths - Please help. Thanks!

            

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hhmami

Rank: 3Rank: 3


105
5#
發表於 05-11-11 00:07 |只看該作者

Re: P4 Maths - Please help. Thanks!

Hi, DSS & Yukyuk,

Thank you so much for your quick answer.

I also use the same method with yours & get the same answer, i.e. 160.  But the correct answer is 20, not 160.   I really don't understand, so will ask my son to check with his teacher tomorrow.  Will update you once get the reply from teacher.

Anyway, thanks again for your help.  

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Swan

Rank: 4


573
6#
發表於 05-11-11 00:16 |只看該作者

Re: P4 Maths - Please help. Thanks!

Please note that the question is asking for the fifth number.  Would the calculation be like this:

a+b+c+d = 60
a+b+c+d+e = 80

so by substitution:

60+e = 80
e = 80-60 = 20

So the fifth number is 20.

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Yukyuk

Rank: 5Rank: 5

醒目開學勳章


4119
7#
發表於 05-11-11 00:21 |只看該作者

Re: P4 Maths - Please help. Thanks!

Please help for the Maths question below:

如果將 "average" 轉為 " total number" 就合理

The total number of 4 numbers is 60. The total number of 5 numbers is 80. What is the fifth number?

Thanks a lot.

Swan 寫道:
Please note that the question is asking for the fifth number.  Would the calculation be like this:

a+b+c+d = 60
a+b+c+d+e = 80

so by substitution:

60+e = 80
e = 80-60 = 20

So the fifth number is 20.

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daisychan

Rank: 5Rank: 5


3465
8#
發表於 05-11-11 00:33 |只看該作者

Re: P4 Maths - Please help. Thanks!

但是 P.4 的 Maths 會唔會咁淺     

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Swan

Rank: 4


573
9#
發表於 05-11-11 00:36 |只看該作者

Re: P4 Maths - Please help. Thanks!

Oh! I forgot the "average".  Sorry!


[quote]如果將 "average" 轉為 " total number" 就合理

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hhmami

Rank: 3Rank: 3


105
10#
發表於 05-11-12 08:05 |只看該作者

Re: P4 Maths - Please help. Thanks!

Hi, DSS & Yukyuk,

The school teacher confirmed that the model answer was wrong.  Our method is right and the correct answer is 160, not 20.

Thanks for your help.

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