Question

At wind speeds above 1000 centimeters per second (cm/sec), significant sand-moving events begin to occur. Wind speeds below 1000 cm/sec deposit sand and wind speeds above 1000 cm/sec move sand to new locations. The cyclic nature of wind and moving sand determines the shape and location of large dunes. At a test site, the prevailing direction of the wind did not change noticeably. However, the velocity did change. Sixty wind speed readings gave an average velocity of x = 1075 cm/sec. Based on long-term experience, σ can be assumed to be 280 cm/sec.

(a) Find a 95% confidence interval for the population mean wind speed at this site. (Round your answers to the nearest whole number.)

lower limit	cm/sec
upper limit	cm/sec

What price do farmers get for their watermelon crops? In the third week of July, a random sample of 42 farming regions gave a sample mean of x = $6.88 per 100 pounds of watermelon. Assume that σ is known to be $1.90 per 100 pounds.

A farm brings 15 tons of watermelon to market. Find a 90% confidence interval for the population mean cash value of this crop. What is the margin of error? Hint: 1 ton is 2000 pounds. (Round your answers to two decimal places.)

lower limit	$
upper limit	$
margin of error	$

Answer 1

a)

sample mean 'x̄=	1075.000
sample size    n=	60.00
std deviation σ=	280.000
std error ='σx=σ/√n=	36.1478

for 95 % CI value of z=		1.960
margin of error E=z*std error =		70.848
lower bound=sample mean-E=		1004.15
Upper bound=sample mean+E=		1145.85

lower limit=		1004
upper limit =		1146

2)

for 2nd problem:

lower limit=				1919.33
upper limit=				2208.67
margin of error=				144.67