A manufacturer reckons that the value of a machine, which costs him $Rs.$ $15625$ will depreciate each year by $20 \% .$ Find the estimated value at the end of $5$ years.
cost of machine $= Rs .15625$
Machine depreciates by $20 \%$ every year.
Therefore, its value after every year is $80 \%$ of the original cost i.e., $\frac{4}{5}$ of the original cost.
$\therefore $ Value at the end of $5$ years $ = 15625 \times \underbrace {\frac{4}{5} \times \frac{4}{5} \times \ldots \times \frac{4}{5}}_{5\,\,\,times} = 5 \times 1024 = 5120$
Thus, the value of the machine at the end of $5$ years is $Rs.$ $5120 .$
The number of terms of the $A.P. 3,7,11,15...$ to be taken so that the sum is $406$ is
Let $S_n$ denote the sum of the first $n$ terms of an arithmetic progression. If $\mathrm{S}_{10}=390$ and the ratio of the tenth and the fifth terms is $15: 7$, then $S_{15}-S_5$ is equal to:
The sum of all those terms, of the anithmetic progression $3,8,13, \ldots \ldots .373$, which are not divisible by $3$,is equal to $.......$.
If the sum of three consecutive terms of an $A.P.$ is $51$ and the product of last and first term is $273$, then the numbers are
A farmer buys a used tractor for $Rs$ $12000 .$ He pays $Rs$ $6000$ cash and agrees to pay the balance in annual instalments of $Rs$ $500$ plus $12 \%$ interest on the unpaid amount. How much will the tractor cost him?