Question

15. The population of a city increases at
a rate of 9% every year. What was the
population of the city 2 years ago, if
its present population is approximately
28,00,000?​

Answer 1

${\large{\bf{\red{\underline{Given :}}}}}$

• The population of a city increases at
• a rate of 9% every year.
• Its present population is 28,00,000.

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${\large{\bf{\blue{\underline{To Find :}}}}}$

• What was population of city after 2 ago.

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${\large{\bf{\orange{\underline{Solution :}}}}}$

Formula to be used:

${\blue{\bigstar{\pink{\boxed{\mathfrak{ \frac{Present \: population \times R \times Time}{100} }}}}}}$

For 1st year decrease :

${\sf{\mapsto{ \frac{Present \: population \times R \times Time}{100} }}}$

${\sf{\mapsto{ {\cancel\frac{2800000 \times 9 \times t}{100} }}}}$

${\blue{\mapsto{\red{\boxed{\bf{2,52,000}}}}}}$

For 2nd year decrease :

${\bf{\purple{The \: total \: population = 28,00,000 - 2,52,000 = 25,48,000}}}$

${\sf{\mapsto{ \frac{Present \: population \times R \times Time}{100} }}}$

${\sf{\mapsto{ {\cancel\frac{3052000 \times 9 \times t}{100} }}}}$

${\blue{\mapsto{\red{\boxed{\bf{2,74,680}}}}}}$

Total decrease in 2 years :

${\sf{\purple{28,00,000 - 5,26,680}}}$

${\blue{\mapsto{\red{\underbrace{\green{\boxed{\bf{22,73,320}}}}}}}}$

So,

The population of city before 2 years was 22,73,320.

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