Answer:
a) The confidence interval is
.
Step-by-step explanation:
We have to calculate a confidence interval (CI) of a difference of proportions.
For the existing procedure, the proportion is:

For the new procedure, the proportion is:

To calculate the CI, we need to estimate the standard deviation

For a 90% CI, the z-value is 1.64.
Then, the CI is:

Total distance covered by <span>George and Carmen
</span>x + y = 350
And they biked 80 kilometers more than they bussed
<span>80 + y = x </span>
Putting the value of x=80 + y in <span>x + y = 350:
</span>We get:
<span>80 + y + y = 350 </span>
<span>2y = 270 </span>
<span>y = 135 km</span>
<span>Substituting y = 135 in x + y = 350 </span>
<span>x + 135 = 350</span>
<span>x = 215 km </span>
Thus George and Carmen biked for 215 km and bussed for 135 km.