The compound interest (in ₹) on ₹ $6250$ at $12 \%$ per annum for $1$ year,compounded half-yearly is

$A$ sum of money at compound interest doubles itself in $15$ years. It will become eight times of itself in (in $years$):

If the ratio of $C.I.$ and $S.I.$ interest for the same principal and rate of interest for $2$ years is $1.2,$ find the rate of interest (in $\%$).

The production of a factory grows at a $8 \%$ $p.a.$ What will be its production (in $lakh$ tonnes) for the year $2010$,if its production in $2008$ was $70$ $lakh$ tonnes?

$A$ man gave $50 \%$ of his savings of ₹ $84,100$ to his wife and divided the remaining sum among his two sons $A$ and $B$ of $15$ and $13$ years of age respectively. He divided it in such a way that each of his sons,when they attain the age of $18$ years,would receive the same amount at $5 \%$ compound interest per annum. The share of $B$ was (in ₹):

$A$ certain sum at compound interest amounts in two years to ₹ $2809$ and in three years to ₹ $2977.54$. Find the rate of interest and the original sum (in ₹).