Question

sum the series 2/5+2.4/5.10+2.4.6/5.10.15​

Answer 1

2/5 + 2*4/5*10+2*4*6/5*10*15

= 2/5 + 16 + 1440

= 2+80+7200/5

= 7282/5

= 1456.4

It is the correct answer

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Answer 2

Answer:

2/3

Step-by-step explanation:

NOTE: I am assuming it's summed up to infinity.

     2/5 + (2*4)/(5*10) + (2*4*6)/(5*10*15) + . . . ∞

=>  2/5 + ( 2/5 ) ² ( 1*2/1*2) + (2/5)³ (1*2*3/1*2*3) +. . . ∞            

                              [taken "2/5" out common from each term in the summation] [also note that the second bracket of each term get cancelled]

=> 2/5 + (2/5)² + (2/5)³ + (2/5)⁴ + . . . ∞

                              [By using sum of a G.P.]

=>    (2/5)  

     (1 - 2/5)

=> 2/3