# Math( 8th) Rate of change

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Khiry has money in a savings account at the bank that increases by the same amount of interesr each year. In 2003 khiry had \$200 in the bank. In 2006, Khiry had \$215 in the bank.In how mnany years will Khiry hav \$230?

The cost of gasoline per gallon in 1989 is \$2.39. In 1995, the cost of gas per gallon is \$2.69. In what year will the cost of gas be \$2.89?

Mr. Jenssen's car decreased in value at a constant rate at the start of each successive year. The casr was worth \$11,000 in 2003 and \$9,600 in 2007. When the car was worth \$8,900, he sold it, In what year did Mr. Jessen sell the car?

• Math( 8th) Rate of change -

Problems 1 and 2\$2.69-\$2.39 don't make it clear how many years but I will assume we subtract 2006-2003 = 3 years.
So the \$200 has grown by \$15 in the 3 year or \$5/year.
Let x = number of years
200 + 0.05x = 230
Solve for x and add to year 2003.

\$2.69-2.39 = 0.30 increase in 6 years (1995-1989) which is 0.05/year.
Let x = number of years.
2.39 + 0.05*x = 2.89
x = (2.89-2.39)/0.05 = 10 years and add that to 1989.

Problem 3 states how the years are to be counted; i.e., at the start of each year. The car is worth \$11,000 at the start of 2003 and at the start of 2007 it was worth %9,600. That's 4 years so it is decreasing at the rate of \$(11,000-9600)/4 = \$350/year.
Let x = number of years.
11,000 - 350x = 8,900
x = 6 years; add that to 2003 so he must have sold the car at the start of the year
2009. Check my work.