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?A. 1525
B. 1200
C. 1750
D. 1800
E. 1400

Option (D) is correct.

Explanation:

Given that,

Total invoices = 30,800

Number of computers = 2

Rate at which invoices produces by first computer = 7,700 per hour

Rate at which invoices produces by second computer = 6,800 per hour

Number of invoices produces by each computer:

= Total invoices ÷ Number of computers

= 30,800 ÷ 2

= 15,400

Now, the time taken by the first computer to reach out its goal of 15,400:

= Number of invoices produces by First computer ÷ Rate of producing invoices

= 15,400 ÷ 7,700

= 2 hours

The total invoices produced by the second computer in 2 hours:

= Rate at which it produces invoices × 2 hours

= 6,800 per hour × 2 hours

= 13,600

So, the number of invoices still need to produce by the second computer is as follows:

= Total invoices produces by second computer - Total invoices produces in 2 hours

= 15,400 - 13,600

= 1,800