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標題: Math problem [打印本頁]

作者: smallfoothk 時間: 12-3-5 17:08 標題: Math problem

1.At least how many factors does a composite number have?Ans:3, why? 2.How many 6-cm squares can be cut from a piece of paper which is a 38-cm square?Ans:36, Why?

作者: thomas_dad 時間: 12-3-5 18:11

回復 smallfoothk 的帖子

I can answer question 1.

For those numbers which can be divided only by 1 and themselves are called "Prime Number", for example,

2 - factors are 1 and 2;
3 - factors are 1 and 3;
5 - factors are 1 and 5;
7 - factors are 1 and 7 and so on.

For those numbers which are even or can be divided not only by 1 and themselves are called "Composite Number", for example,

4 - factors are 1, 2 and 4;
6 - factors are 1, 2, 3 and 6;
8 - factors are 1, 2, 4, and 8;
10 - factors are 1, 2, 5, and 10;
12 - factors are 1, 2, 3, 4, 6, and 12 and so on.

thomas_dad

作者: LingChiBaBa 時間: 12-3-5 23:57

本帖最後由 LingChiBaBa 於 12-3-5 23:59 編輯

For Question 2,

I think the question is the paper is 38cm per side and the paper piece is 6 cm per side.

Since the cut piece is 6cm-square, 38cm per side which is divided by 6cm that 6 pieces can be cut out and remained 2cm which is scarped.

Therefore, number of 6cm-square paper can be cut is 6 x 6 = 36 pieces.

作者: Unclejt 時間: 12-3-6 01:09

Ask your son/daughter to do the problem when the paper is smaller, say, 15 cm x 15 cm.

Draw an appropriate picture to help him/her understand the trick.

Ask him/her to generalize the argument to the present setting.

Ask him/her what'll happen if the paper is rectangular, say, 40 cm x 56 cm.

作者: smallfoothk 時間: 12-3-6 12:10

回復 Unclejt 的帖子

thanks,Ans is 6

作者: hkmom 時間: 12-3-6 13:52

回復 smallfoothk 的帖子

No wor! Pls see below.

15cm x 15cm paper

15 / 6 = 2.5 => so only 2 counts of "6 cm" can result per side
Hence, the maximum no. of 6-cm squares that can be cut from a 15cm x 15cm paper is 2 x 2 = 4.

40cm x 56cm paper

40 / 6 = 6.67
56 / 6 = 9.33
Hence, the maximum no. of 6-cm squares that can be cut from a 40cm x 56cm paper is 6 x 9 = 54.

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