a person hired a firm to build a cb tower. the firm charges $100 for labor for the first 10 feet. After that, the cost of the labor for each succeeding 10feet is $25 more than the proceding 10 feet. That, is the next 10 feet will cost $12, the next 10 feet will cost $150, etc. How much will it cost to build a 90-foot tower.
If I understand this correctly, the first ten feet is $100. This leaves 80 remaining feet to be built. If the initial part of your question is what the answer needs to be based upon, feet 11-20 will cost $125, 21-30 will cost $150, 31-40 will cost $175, 41-50 will cost $200, 51-60 will cost $225, 61-70 will cost $250, 71-80 will cost $275, and 81-90 will cost $300.
The entire tower will cost $1800. (This number is the sum of all of the different costs per 10 feet.)
The discussion topic is more suited to be included in Q&A Maths Section, however the answer is a under:
The cost of initial 10 feet is $100 and each subsequent 10 feet cost $25 higher. Thus the cost of each 10 feet of 9x10feet tower will be in arithmatic progression with common difference of $25. The costs will be as 100,125,150,...,300. The sum of these costs is given by the formula N(n1+nN)/2 where N is the number of terms, n1 is the first term and nN is the last term. The total cost is therefore 9(100+300)/2 or $1800.