sandy wrote:

In a factory, machine A operates on a cycle of 20 hours of work followed by 4 hours of rest,and machine B operates on a cycle of 40 hours of work followed by 8 hours of rest. Last week, the two machines began their respective cycles at 12 noon on Monday and continued until 12 noon on the following Saturday. On which days during that time period was there a time when both machines were at rest?

Indicate all such days.

A. Monday

B. Tuesday

C. Wednesday

D. Thursday

E. Friday

F. Saturday

Let's focus on 1 machine at a time and list the starting and stopping time.

We'll start with

Machine AMONDAY12 noon:

Machine A startsTUESDAY8:00 am:

Machine A stops12:00 noon:

Machine A startsWEDNESDAY8:00 am:

Machine A stops12:00 noon:

Machine A startsTHURSDAY8:00 am:

Machine A stops12:00 noon:

Machine A startsFRIDAY8:00 am:

Machine A stops12:00 noon:

Machine A startsSATURDAY8:00 am:

Machine A stops12:00 noon:

Machine A starts------------------------------------------------------

Now let's add

Machine BMONDAY12 noon:

Machine A starts12 noon:

Machine B starts TUESDAY8:00 am:

Machine A stops12:00 noon:

Machine A startsWEDNESDAY4:00 am:

Machine B stops8:00 am:

Machine A stops12:00 noon:

Machine A starts12:00 noon:

Machine B startsTHURSDAY8:00 am:

Machine A stops12:00 noon:

Machine A startsFRIDAY4:00 am:

Machine B stops8:00 am:

Machine A stops12:00 noon:

Machine A starts12:00 noon:

Machine B startsSATURDAY8:00 am:

Machine A stops12:00 noon:

Machine A startsAs we can see, both machines are stopped at the same time on Wednesday and Friday.

_________________

Brent Hanneson – Creator of greenlighttestprep.com

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