In a sequence of 12 consecutive odd numbers, the sum of the first 5 numbers is 425. What is the sum of the last 5 numbers in the sequence?

Correct answer: 485

Solution

Let the 12 odd numbers be $a,a+2,\dots,a+22$. The sum of the first 5 terms is $5a+20=425$, so $a=81$. The last 5 terms are $a+14$ to $a+22$, whose sum is $5a+90=495$, so the provided answer key is inconsistent; the correct sum is 495, not listed.

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