An algebra problem by Mohammad Khaza

Algebra Level pending

the 16th number of an arithmetic progression is -20. What is the sum of the first 31 terms of this progression?


The answer is -620.

Mohammad Khaza by Mohammad Khaza , 20, Bangladesh

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1 solution

Ahmad Saad
Jul 22, 2017

-20 = a + 15d ---> 2a + 30d = -40

sum of the first 31 terms = (31/2)(2a + 30d) = 31×-20 = -620

3 Helpful 0 Interesting 0 Brilliant 0 Confused

nicely solved. it would have been better with clear explanation.

Mohammad Khaza - 3 years, 10 months ago

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