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I'll show you how to use this idea in my sequence: 8, 13, 18, ..., 88. You can see that a = 8 and d = 5. I want to know what term has the value 88. So I use the idea above a + dn = (n+1)^{th} term and I substitute in the values I know:
Now I solve for n:
Since this is the (n+1)^{th} term, this is the 17^{th} term in the sequence. Now you try it the same way with your sequence. Hope this helps
Jesse, Each successive term is obtained by adding 3 to the previous term so you need to find out how many 3's get you from 51 to 75. Try it with 48 then 45 then 42 to get yourself going. Penny  


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