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3 years ago

An arithmetic progression has first term 11 and Fourth term 32. Fine the sum of the first nine term

Mathematics

2 answers:

bonufazy [111]3 years ago

6 0

Answer:351

Step-by-step explanation:Try to plus the same number every time, I used 7 and it worked. : )

schepotkina [342]3 years ago

4 0

Let the first term be a, 4th term be $a_{4}$ , difference between terms be d, and sum of first nine terms be $S_{9}$ .

$a_{4}$ = a + 3d

32 = 11 + 3d

3d = 32 - 11

3d = 21

d = 7

$S_{9}$ = $\frac{9}{2} (2a + (9-1)d)$

= $\frac{9}{2} (22+56)$

= 9(11+28)

= 9(39)

= 325

Sum of first nine terms is 351.

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