Question

The mean weight of college students is 154 lbs and the standard deviation is 3 lbs.

Assuming that the weight is normally distributed, determine the following percentages.
145 148
151
154 157 160 163
DO NOT write % in the box. It is already written outside the box for you"
The percentage of college students who weigh...
30
1)...less than 157 is
%
2) greater than 148 is
3)...between 145 and 160 is
%
%

Answer 1

Answer:(approx) 6.

Step-by-step explanation:Here μ=51 and σ=15

Z=

σ

X−μ

​

=

15

X−151

​

When X=120, Z=

15

120−151

​

=−2.067

When X=155, Z=

15

155−151

​

=0.2667

When X=185, Z=

15

185−151

​

=

15

35

​

=2.2667

(i) P(120<X<155)=P(−2.07<Z<0.27)

=∫

−2.067

0.2667

​

ϕ(z)dz=∫

0

0.2667

​

ϕ(z)dz+∫

0

2.0667

​

ϕ(z)dz

=0.4803+0.1026=0.5829.

Here N=500

∴ The number of students whose weight is between 120 and 155 pounds is

0.5872×500=291

(ii) P(X<185)=P(Z>2.27)=∫

2.2667

∞

​

ϕ(z)dz

=∫

0

∞

​

ϕ(z)dz−∫

0

2.2667

​

ϕ(z)dz=0.5−0.4881=0.0119

∴ the number of students with weight about 185 pounds.

=0.0119×500= (approx) 6.