Mary gets an oil change for her car every 3750 miles and a tire rotation every 6000 miles. What is the mileage of the car at the first time she gets both an oil change and a tire rotation at the same time?
We're looking for the LCM of 3750, and 6000. the way I would do it is find the GCD of the two numbers, then multiply 3750 and 6000 together and divide it by the GCD:
6000-3750=2250
3750-2250=1500
2250-1500=$\boxed{750}$
$\dfrac{3750\cdot6000}{750}=5\cdot6000=\boxed{30,000 }$ miles