Maths MC(need detailed steps)

1.) The scale of a map is 1:200. If two buildings are 3.8 cm apart
on the map, then the acutal disance between the two buildings is
(detailed steps needed)

Ans:
Real Distance : 3.8*200 cm=3.8*2 m =7.6m=0.0076 km// (A)


2.)If the area of a regular 10-sided polygon is 123 cm^2, find the
lenghth of the side of the 10-sided ploygon. Give the answer correct
th the nearest 0.1 cm.

Ans:

first , we need to find out the radius .
let the radius = r cm ,
then we cut the 10-sided polygon into 10 triangle.
so that the area of each triangle = 123/10 = 12.3 cm^2
be the law of area , we have 12.3 = (1/2)(r)(r)(sinθ)
=>12.3=(1/2)(r^2)(sin 36)
=>r=6.47 cm .
by cosine law ,
(length of each side )^2 = r^2+r^2-2r^2*cos36
=>length of each side=4 cm // (B)

3.)The mean weight of 36 boys and 32 girls is 46kg. If the mean weight of the boys is 52kg, then the mean weight of the girls is

the mean weight of all people =[ (number of boys)(The mean weight of boys)+(number of girls)(The mean weight of girls)]/(total number of peopeles)]
=> 46=[36*52+32*(The mean weight of girls)]/48
=>The mean weight of girls=...

Maths MC(need detailed steps)
1.) The scale of a map is 1:200. If two buildings are 3.8 cm apart
on the map, then the acutal disance between the two buildings is
(detailed steps needed)
A. 0.076 km
B. 076km
C. 7.6km
D. 76km


2.)If the area of a regular 10-sided polygon is 123 cm^2, find the
lenghth of the side of the 10-sided ploygon. Give the answer correct
th the nearest 0.1 cm.
(detailed steps needed)
A. 3.9cm
B. 4.0cm
C. 6.8cm
D. 8.0cm





2008-12-27 21:46:03 補充：
4.Ans:
P(at least one dart hitting the target)
=1-P(none of darts hitting the targets)
=1-(1-0.2)(1-0.3)
=1-0.8*0.7
=0.44 //(B)