====== Question 10 Exercise 4.2 ======
Solutions of Question 10 of Exercise 4.2 of Unit 04: Sequence and Series. This is unit of A Textbook of Mathematics for Grade XI is published by Khyber Pakhtunkhwa Textbook Board (KPTB or KPTBB) Peshawar, Pakistan.

=====Question 10=====
The population of a town is decreasing by $500$ inhabitants each year If its population in 1960 was 20135, what was its population in 1970? GOOD
====Solution====
Suppose $a_1$ represents the population in 1960. Then
$$a_1=20135.$$
Decrease in population each year=$d=-500$.

The given problem is of A.P and we have to find population in 1970, that is, $a_{11}$.

As we know
\begin{align}
a_{11}&=a_1+10d \\
&=20135+10(-500)\\
&=15135. \end{align}
Hence the population of the town in $1070$ was $15135$. GOOD



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