If the half life of substance is 5 years, then the total amount of the substance left after 15 years, when initial amount is 64 gms is

If $$\log _2 x+\log _4 x+\log _8 x+\log _{16} x=\frac{25}{36}$$ and $$x=2^{\mathrm{k}}$$ then $$\mathrm{k}$$ is

The approximate value of $$\log _{10} 998$$ is (given that $$\log _{10} \mathrm{e}=0.4343$$ )

If the population grows at the rate of $$8 \%$$ per year, then the time taken for the population to be doubled is

(Given $$\log 2=0.6912$$)