Every fifth student who walked into the middle school was surveyed to determine his or her favorite subject. Out of 150 students, 90 students stated that they like math class best. The staff concluded that about 60% of students like math class best. Is the sample method valid? Justify your answer. a)

The conclusion is invalid. This is a biased voluntary response sample.

b)

The conclusion is invalid. This is a biased convenience sample.

c)

The conclusion is valid. This is an unbiased systematic random sample.

d)

The conclusion is valid. This is an unbiased simple random sample.

C

Step-by-step explanation:

d. $180

step-by-step explanation:

if the dimensions of the room is 9ft by 12 ft, we have the area of the floor as,

so the area of the floor is 108 square feet, converting that into square yards we get,

the cost of carpet is $15 per square yard, therefore the cost of carpet for 12 square yards is,

hence, the cost of carpet is $180.

assuming the dimensions of the room be,

15 ft by 12 ft

so, the area of the floor of that room is,

we can convert 180 square feet into square yards, we know that,

1 sq ft = 0.111 sq yard

so, 180 square feet is,

so the area of floor is 20 square yards.

now, the cost of carpet is 15 dollars per square yard, therefore the cost of carpet for 20 square yards is,

so, it will cost $300.