30 TABLETS

We are given that 0.025 mg drug is present in 1 tablet. This means that 120 tablets will have:

120 * 0.025 = 3 mg total drug in them.

So now we are given that 0.1 mg of drug is present in one new tablet.

The total amount of drug should be 3 mg as we need the same amount of drug.

If 0.1 mg is in 1 tablet then:

Total tablets would be = 3/0.1 = 30 tablets

So the answer = 30 tablets