Sum of Multiples Prepswift Q2

Can someone explain if there’s a way to do this problem more efficiently than just plugging in numbers?

Multiples of 10 must be 10 apart, and multiples of 9 must be 9 apart right? For which of these can we fit in more of within a limited area?

That makes sense but the answer is D.

We still need to consider the endpoints and the length though right?

What if both the first and last values are each multiples of 10? For example from 10 to 20, there will be two multiples of 10 but only one of 9

Ahh okay, I see your point. Thank you!

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