Answer:
We need at least 271 transactions
Step-by-step explanation:
In a sample with a number n of people surveyed with a probability of a success of
, and a confidence level of
, we have the following confidence interval of proportions.

In which
z is the zscore that has a pvalue of
.
The margin of error is:

90% confidence level
So
, z is the value of Z that has a pvalue of
, so
.
Minimum sample size within five percentage points.
n when M = 0.05.
We dont know the proportion, so we use
, which would be the proportion requiring the largest sample size






Rouding up
We need at least 271 transactions