Dimensional formula for activity of a radioactive substance is

The true length of a wire is $$3.678 \mathrm{~cm}$$. When the length of this wire is measured using instrument $$A$$, the length of the wire is $$3.5 \mathrm{~cm}$$. When the length of the wire is measured using instrument $$B$$, it is found to have length $$3.38 \mathrm{~cm}$$. Then, the

The Vernier scale of a travelling microscope has 50 divisions which coincides with 49 main scale divisions. If each main scale division is $$0.5 \mathrm{~mm}$$, then the least count of the microscope is

A cylindrical wire has a mass $$(0.3 \pm 0.003) \mathrm{g}$$, radius $$(0.5 \pm 0.005) \mathrm{mm}$$ and length $$(6 \pm 0.06) \mathrm{cm}$$. The maximum percentage error in the measurement of its density is

If $$P, Q$$ and $$R$$ are physical quantities having different dimensions, which of the following combinations can never be a meaningful quantity?