Sally has caught covid but doesn’t know it

If I have the following Hypothese:

H1: Women tend to watch romantic films more than men 

Apparently it's a chi-square because I'm measuring relationships between expected frequency and Observed frequency and also because Gender is on the nominal level. But what if this is designed for a survey in which questions are on the nominal, Ordinal and interval level (Likert scale - differential sementic) will the outcome still be a Chi-square?

Find the critical points for the function f (x) = x sin−1 x on the interval [−1, 1]. Identify the
absolute maximum and absolute minimum values. State the intervals for where the functions is increasing,
decreasing.

In a survey, several people were asked how many years it has been since they purchased a mattress. The results are shown in the table.

Evaluate the following (Express the answer in 2 decimal places):

a) Standard deviation (4 Marks)

b) Coefficient of variation (1 Mark)

c) Expected value of x, that is E(x) (2 Marks)

d) Variance of x, that is Var(x)(3 Marks)

e) The probability of having bought a mattress in the last 3 years. (1 Mark) 

Proving that the set of units of a ring is a cyclic group of order 4
The set of units of ${\displaystyle \frac{\mathbb{Z}}{10}\mathbb{Z}}$ is ${\displaystyle \{\bar{1},\bar{3},\bar{7},\bar{9}\}}$, how can I show that this group is cyclic?
My guess is that we need to show that the group can be generated by some element in the set, do I need to show that powers of some element can generate all elements in the other congruence classes?
For example $7^2=49\equiv 9\pm \mathrm{mod}10$, i.e. using 7 we can generate an element in the congruence class of 9, but can not generate 29 for example from any power of 7, so is it sufficent to say that an element is a generator if it generates at least one element in all other congruence classes?

I need solution of Q2 of given assignment

In each part suppose that the augmented matrix for a system of linear equation has been reduced by row operations to the given row echelon form. Solve the system