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Examples 11 to 15

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(11) The value of  a machine depreciates at the rate of  10 %  per annum. If its present value is Rs. 8100, what will be its worth after 2 years ?  What was the value of  the machine  2 years ago ?

Soln.

Value of  the machine after  2 years

=     8100    \times \left (1-\frac{10}{100} \right ) ^{2}

=     8100\times \frac{90}{100} \times \frac{90}{100}    =   Rs.  6561

Value of  the machine  2 years  ago

=   \frac{8100}{\left (1-\frac{10}{100} \right ) ^{2}}

=     8100 \times \frac{100}{90} \times \frac{100}{90}     =  Rs.  10000

(12) What will be  80%  of  a number whose 200%  is 90?

Soln. Here,  200  %  =  90

\therefore  80  %   =  36

(13) 20 % of  a number when added to 20 is equal to the number.  What is the number ?

Soln. Here,  80  %  =  20

\therefore 100  %   =  25

\thereforeThe number  =  25.

(14) A fruit seller had some oranges. He sold 30  % and still had 560 left. How many oranges did he originally have ?

Soln. Here,  70  %  =  560

\therefore 100  %   =  800

\therefore Originally he  have  800  oranges..

(15) A man spends Rs. 4500 per month and saves 10 %  of  his income. Determine his monthly income.

Soln. Here,  90  %  =  4500

\therefore 100  %   =  5000

\therefore His monthly salary  =  Rs. 5000

 

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