It takes Tammy 15 minutes to do one oil change, and it takes Jill 10 minutes. At 2:30 pm, they both finish an oil change simultaneously. If Tammy and Jill both began doing oil changes at exactly the same time and worked without pausing, when did they both start doing oil changes?
Choose the correct choice from the following:
A) 2:00 pm
B) 2:05 pm
C) 2:10 pm
D) 2:15 pm
E) 2:20 pm
Since Tammy finishes s oil changes after s × 15 minutes and Jill finishes c oil changes after c × 10 minutes, they both finished doing an oil change at the same time when s × 15 = c × 10. Since s and c must be integers (they represent the number of oil changes finished) this question is asking you to find a common multiple of 15 and 10. The question asks for the first time they began a car simultaneously, so you must find the least common multiple and subtract. The least common multiple of 15 and 10 is 30, so in the context of the question, this would be 30 minutes. Therefore, they began changing the oil of a car at the same time at 2:30 - 30 minutes, or 2:00 p.m. The answer is (2:00 pm).
<result>A</result>
It takes Tammy 15 minutes to do one oil change, and it takes Jill 10 minutes. At 2:30 pm, they both finish an oil change simultaneously. If Tammy and Jill both began doing oil changes at exactly the same time and worked without pausing, when did they both start doing oil changes?