Answer:

10 (A)

Step-by-step explanation:

Observe that:

Multiples of 20 - 20, 40, 60, 80, 100, ...

Multiples of 50 - 50, 100, 150, 200, 250, ...

Then, the LCM of 20 and 50 is 100.

Multiples of 30 - 30, 60, 90, 120, 150, ...

Multiples of 45 - 45, 90, 135, 180, 225, ...

Then, the LCM of 30 and 45 is 90.

Thus, 100 - 90 = 10.

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