Question

The income of a person is rs. 3,00,000 in the first year and he recieves an increase of rs. 10,000 to his income per year for the next 19 yrs. find the the total amount? he received in 20 years???

Answer 1

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This can be solve by A.P

A= 300000
D = 10000

n = 20

using sum formula ,

S20 =
$\frac{20}{2} \times (600000 + 19 \times 10000) \\ = 10(790000) \\ = 7900000$


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Answer 2

Answer:

Income of the person in 1st year = Rs 3,00,000

Income of the person in 2nd year= Rs 3,00,000 + 10,000

                                                       = Rs 3,10,000  

Income of the person in 3rd year= Rs 3,10,000 + 10,000

                                                       = Rs 3,20,000

Thus, income received per year is

300000, 310000, 320000,..........................

This is an AP as a difference between consecutive term is constant.

300000, 310000, 320000,.......................

Here,

First term = a = 300000

Difference = 310000 - 300000

                  = 10000

Sn = N/2 ( 2a + (n - 1)d)

S20 = 20/2 ( 2*300000 + (20-1)10000)

       = 10 ( 600000 + 19* 10000)

       = 10 ( 600000 + 190000 )

       = 10 * 790000

       = 7900000

Thus, the total amount received at the end of 20 years is Rs 7900000.