The formula for the sum of an arithmetic series is expressed as:
Sn=n/2(a1+an)
where:
n=total terms
a1=the initial term
an=the final term
given
n=18, an=275, Sn=4185
substituting these values into the equation results in:
4185=18/2(a1+275)
after simplification, we obtain:
4185=9(a1+275)
dividing by 9 yields:
465=a1+275
therefore
a1=465-275
a1=190
Conclusion: the first term is 190
The diver descends, resulting in a movement downwards of −20 feet. Begin with 20 negative tiles and divide them into 5 equal sets. Each set contains 4 negative tiles, indicating he descended at a speed of −4 feet per second.