Just trying to double check my work here ...

Situation: Anne Teak, the financial manager of a furniture manufacturer, is considering operating a lock-box system. She forecasts that 400 payments a day will be made to lock boxes with an average payment size of $2,000. The bank's charge for operating the lock boxes is $.40 a check. The interest rate is .015 percent per day.

Math:

1 DAY:
400*2000 = 800,000
800,000*.015 = 12,000
.40*400 = 160.
12,000-160 = 11,840
800,000-11,840 = 788,160

2 DAY:
800,000*2 = 1,600,000
1,600,000*.015 = 24,000
400*.4 = 160.
24,000-160 = 23,840
1,600,000-23,840 = 1,576,160


Questions & Answers:

If the lock box saves 2 days in collection float, is it worthwhile to adopt the system?
Given the daily return it is worthwhile to adopt the system

What minimum reduction in the time to collect and process each check is needed to justify use of the lock-box system?
Given the amount of the daily return, there is no minimum reduction in the time needed to collect and process each check to justify use of the lock-box system.

How did I do?