10 feet will cost $150, etc. How much will it cost to build a 90-foot tower?

For the first 10 feet charge = $100

For the (2nd) 10 feet charge = $125

For the (3rd) 10 feet charge = $150

For the (4th) 10 feet charge = $175

For the (5th) 10 feet charge = $200

For the (6th) 10 feet charge = $225

For the (7th) 10 feet charge = $250

For the (8th) 10 feet charge = $275

For the (9th) 10 feet charge = $300 Therefore, the cost to build a 90-foot tower is the sum of all above (each 10 feet):

100+125+150+175+200+225+250+275+300 =$ 1800. Hence, the cost for a 90-foot tower will be $1800.

A person deposited $500 in a savings account that pays 5% annual interest that is compounded yearly. At the end of 10 years, how much money will be in the savings account? 5% when converted into a decimal is .05. Dividing 100 into 5 equals 20. After multiplying the decimal (.05) times 500, the answer is 25. Therefore, each year the account will have accumulated $25 in interest. Multiply $25 by 10 (year period) equals $250. At this point, add the initial deposit of $500 + $250 = $750. The answer is at the end of 10 years, there will be $750 in the savings account.

Finally, because these mathematical statements are always going to be true given the scenarios, they are referred to as tautology. (Bluman, 2011)

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Reference:

Bluman, A. G. (2011). Mathematics in our world (1st ed. Ashford University Custom). United States: McGraw-Hill