Answer:
There were 480 customers on Friday.
To calculate the increase from Thursday to Friday, we can use the following formula:
```
Increase = (percent increase / 100) * starting value
```
In this case, the percent increase is 1/5, and the starting value is 400 customers. So, the increase is:
```
Increase = (1/5 / 100) * 400 = 8
```
This means that there were 8 more customers on Friday than there were on Thursday. So, the total number of customers on Friday is:
```
Total = Starting value + Increase
= 400 + 8
= 480
```
Explanation: