In an arithmetic series, S20=670, and u20=62. a) What is the first term, u1? b) What is the common difference, d?

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The sum of the first 20 terms is 670, and the 20th term is 62. As this is an arithmetic sequence, we know the difference between each term will be d. u is the term, n is the number of term.
a) What is the first term, u1?Sn= n/2 x (u1+un)S20 = n/2 x (u1+u20) = 20/2 x (u1+ 62) 670 = 10 x (62 + u1) = 620 + 10u1(670 - 620) = 10u150 = 10u1, u1 = 5
b) What is the common difference, d?un= u1+(n-1)du20= u1+19d62 = 5 + 19d57 = 19dd = 3

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