14 + 28 + 42 + 56 + … 280
= 14 (1 + 2 + 3 + 4 + … + 20)
= 14 × 20 × 21 / 2
= 2940
where we use the well-known identity,

1st Bagel; $0.79. 2nd Bagel; $0.67. 3rd Bagel; $0.70. 4th Bagel; $0.75. So B would be the correct answer, given 67¢ is cheaper ;)))))))
We have
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A B C D E
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1 yard
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1/5 yard ------------------
7/10 yard
<span>The distance poles B and D= (1-1/5)=4/5 yard
</span>The distance poles B and E= BD+DE=4/5+7/10=(8+7)/10=15/10=3/2 yard
the answer is 3/2 yard (distance poles B and E)