Mathematics · Sequences and series (arithmetic progression)
Find the sum of the first 20 terms of the arithmetic progression 3, 7, 11, ...
A. 780
B. 800
C. 820
D. 860
Reply with your answer and how you got it, then check below.
Find the sum of the first 20 terms of the arithmetic progression 3, 7, 11, ...
A. 780
B. 800
C. 820
D. 860
Reply with your answer and how you got it, then check below.
Answer: C
a = 3, d = 4, n = 20.
S = n/2 [2a + (n - 1)d] = 10 x [6 + 19 x 4] = 10 x 82 = 820.
A common slip is using
d instead of (n - 1)d, which gives 860.
Read more: New General Mathematics for West Africa: sequences and series
a = 3, d = 4, n = 20.
S = n/2 [2a + (n - 1)d] = 10 x [6 + 19 x 4] = 10 x 82 = 820.
A common slip is using
d instead of (n - 1)d, which gives 860.Read more: New General Mathematics for West Africa: sequences and series