(a). Paint from clothes -
x | x - | (x - )2 | |
4.0 | - 0.3 | 0.09 | |
4.2 | - 0.1 | 0.01 | |
4.4 | 0.1 | 0.01 | |
4.6 | 0.3 | 0.09 | |
17.2 | 0.2 |
Total number of data points, N = 4
Mean value of %T of paint from clothes:
= x / N
= (4.0 + 4.2 + 4.4 + 4.6) / 4
= 4.3
Standard deviation, S.D =
=
=
= 0.22
Relative standard deviation = S.D / * 100
= 0.22 / 4.3 * 100
= 5.1 %
Paint from Car -
x | x - | (x - )2 | |
4.5 | - 0.54 | 0.2916 | |
5.3 | 0.26 | 0.0676 | |
5.5 | 0.46 | 0.2116 | |
5.0 | - 0.04 | 0.0016 | |
4.9 | - 0.14 | 0.0196 | |
25.2 | 0.592 |
Mean value of %T of paint from car:
= x / N
= 25.2 / 5
= 5.0
Standard deviation, S.D =
=
= 0.34
Relative standard deviation = S.D / * 100
= 0.34 / 5.0 * 100
= 6.8%
(b). S1 = 0.22 , N1 = 4
S2 = 0.34, N2 = 5
Pooled standard deviation,
= [(4-1)*0.222 + (5-1)*0.342] / (4+5-2)
= [( 3*0.0484 + 4*0.1156 ) / 7]
= (0.1452 + 0.4624) / 7
= 0.0868
= 0.29
The composition of a flake of paint found on the clothes of a hit-and-run victim was...