Question

A security business invoices its 30,800 customers on the first day of each month, with each of two computers doing half the job. one invoicing machine produces at the rate of 7,700 per hour, and the other at the rate of 6,800 per hour. when the first computer finishes its run, how many invoices did the second computer still need to produce?

Answer 1

Total number of invoices = 30,800
Invoices produced by each computer = 30,800/2 = 15,400
Rates:
Computer 1 = 7,700/hr
Computer 2 = 6,800/hr

Time taken by computer 1 = 15,400/7,700 = 2 hrs

In 2 hrs, invoices produced by computer 2 = 2*6,800 = 13,600
Invoices remaining after the two hours when computer 1 finishes = 15,400 - 13,600 = 1,800 invoices.