$\text{(i) The null hypothesis H$_0$ : μ = 70. Alternative hypothesis H$_1$ : μ ≠ 70} \\$ $\text{(ii) Calculation of test statistic: Since sample size is large; Z = $\frac{(\bar{X} -μ)}{(\frac{σ}{\sqrt{n}})}$ = $\frac{(71.8-70)}{(\frac{7.8}{\sqrt{100}})}$ = 2.31} \ $ $\text{(iii) Level of significance : α =0.05} \ $ $\text{(iv) Critical value : the value of Z$_α$ at 5% level of significance = 1.96} \ $ $\text{(v) Decision : since the calculated value of |Z| =2.31 is greater than the table value Z$_α$=1.96. The null hypothesis is rejected} \ $