Question

A sequence of numbers starts with 3 and each subsequent number is obtained by adding 5 to the previous number. If the 10th number in the sequence is 53, what is the 20th number in the sequence?
GPT 3.5
Let the first term be $a$ and the common difference be $d.$ The $10$th term is $a+9d=53$. Thus $a+9d=53 \implies a=53-9d.$ Hence, the $20$th term is $a+19d=(53-9d)+19d=\boxed{215}.$

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