Question

7+14+21+..........+140=​

Answer 1

Answer:

770

Step-by-step explanation:

7+14+21+28+35+42+49+56+63+70 = 385 +385 =770

Answer 2

Answer:

1470 is the answer.

Step-by-step explanation:

a1 = 7

a2 = 14

d = 14 - 7 = 7

an = 140

an = a + (n - 1) d

140 = 7 + 7n - 7

n = 140 / 7

n = 20

Sn = n/2 ( a + an )

S20 = 20/2 ( 7 + 140 )

S20 = 10 ( 147 )

S20 = 1470.

Hope it helped.............................

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