SOLUTION: Please help me to solve this numbers 50,51,52...70 using this formula SN=N/2(a1+an)

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Question 1118741: Please help me to solve this numbers 50,51,52...70 using this formula SN=N/2(a1+an)
Found 2 solutions by josgarithmetic, ikleyn:
Answer by josgarithmetic(39618) (Show Source):
You can put this solution on YOUR website!
You have the sequence and you have the formula for what you want. Nothing more needed.

You KNOW already, it is Arithmetic Sequence, according to general term for index n. You can determine how many terms are in your given sequence. Next, just USE THE CORRECT SUMMATION FORMULA.

Answer by ikleyn(52788) (Show Source):
You can put this solution on YOUR website!
.
You just have a formula, and you are given that a1 = 50 and an = 70.

The only thing that you don't know is the number of terms from 50 to 70.

Using fingers of your hands, calculate this number.

Then use the formula.

That's all.

Boldly move forward !

Good Luck ! !