3條英文數學題...F.1

1) The HCF of 36 and 84:
=12(cm)
2) The HCF of 45 and 72:
=9
3) 12:00+(The LCM of 18 and 27):
=12:00+54mins
=12:54(p.m.)

凡係提到largest或者greatest既數就係Highest Common Factor(H.C.F)
而提到Smallest或者好似第三條題目類型既數就係Lowest Common Multiple(L.C.M).

2007-08-10 11:27:53 補充：
li幾條都肯定岩,信吾信由你lu!

1) A rectangle 36 cm by 84 cm is to be covered with spuares which are of the same size.Find the largest size of the squares that can be used to exactly cover the rectangle.

The length of the largest square used is the highest common factor (HCF) of 36 and 84
36 = 2 x 2 x 3 x 3
84 = 2 x 2 x 3 x 7
The HCF is 2 x 2 x 3 = 12
the length of the largest square used = 12 cm, the area of the square used = 12 x 12 = 144 cm²
As the rectangle size is 36cm by 84 cm, that means 3 squares along the shorter length and 7 square along the longer length; and a total of 3 x 7 = 21 square is used to cover the rectangle.
(understand?)


2)A number can divide 45 and 72 exactly. Find the greatest possible value of thie number.
The answer is highest common factor(HCF) of 45 & 72
45 = 3 x 3 x 5
72 = 2 x 2 x 2 x 3 x 3
The HCF is 3 x 3 = 9
The answer is 9.
Test the answer,
45 ÷ 9 = 5
72 ÷ 9 = 8
that means 9 can divide 45 and 72 exactly.

3)Bell A is rung at 18-min interval, while Bell B is rung at 27-min interval. If they are rung together at 12:00 noon, at what time will they be next rung together?
The answer is the LCM of 18 & 27
18 = 2 x 3 x 3
27 = 3 x 3 x 3
The LCM is 2 X 3 X 3 X 3 = 54
the bells will ring together again 54 minutes after 12:00 noon, i.e., 12:54 in the afternoon.

1)84x84=7056cm
2)=13
This all.And sorry I can't either know Q3