Kala purchased a prepaid phone card for $30. Long distance calls cost 9 cents a minute using this card. Kala used her card only once to make a long distance call. If the remaining credit on her card is$28.83 , how many minutes did her call last?

The call lasted 13 minutes

Step-by-step explanation:

In this question, we are told to find the number of minutes a call lasted.

The initial amount on the card is $30 and after making a phone call just once, the balance went down to $28.83

What was used would be 30 - 28.83 = $1.17 or simply 117 cents

Now these long calls come at a cost of 9 cents per minute and we have a total of 117 cents here; the number of minutes is thus 117/9 = 13

This means Kala spent 13 minutes on the call

Her call lasted 13 minutes.

Step-by-step explanation: Kala purchased a prepaid card with $30 worth of talk time. For long distance calls, the card is charged (deduction) 9 cents per minute.

At the time Kala had only $28.83 left on her prepaid card, she had spent the following;

Call charge = 30.00 - 28.83

Call charge = 1.17

Since the calls are charged in cents, we shall convert the amount spent to the appropriate unit, which is cents.

Note that $1.17 equals 117 cents (1.17 x 100).

A minute’s call would cost 9 cents, and this means a call that cost 117 cents can be calculated as follows;

Charge per min = Total charge/9

Charge per min = 117/9

Charge per min = 13

Therefore her call lasted for 13 minutes.

part a

answer: a reasonable domain is where n is a real number. so n can be between 0 and 10. both endpoints are included.

work shown:

n is the number of days after the experiment starts. the smallest n can be is n = 0 which means that 0 days have gone by, and we're at the start. to find out how large n should be, then replace f(n) with 16.13 and solve for n. use logarithms to isolate the exponent.

f(n) = 12*(1.03)^n

16.13 = 12*(1.03)^n

16.13/12 = (1.03)^n

1.34416666666667 = (1.03)^n

(1.03)^n = 1.34416666666667

log[ (1.03)^n ] = log[ 1.34416666666667 ]

n*log[ 1.03 ] = log[ 1.34416666666667 ]

n = log[ 1.34416666666667 ]/log[ 1.03 ]

n = 10.0062999823929

this rounds to n = 10 which is fairly close but not 100% perfect. so this is the largest n can be.

note: if you plug n = 10 into f(n), you'll get roughly 16.127 which rounds to 16.13 (this comes up again in part c)

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part b

answer: the y intercept is 12. it represents the starting height of the plant in cm.

work shown:

plug n = 0 into the f(n) function. simplify

f(n) = 12*(1.03)^n

f(0) = 12*(1.03)^0

f(0) = 12*(1)

f(0) = 12

on day n = 0, aka the starting point, the height f(n) is 12 cm

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part c

answer: the average rate of change is approximately 0.43061036458991 (round however you need to). this represents the average growth rate from day n = 3 to day n = 10. so the plant grew roughly 0.43 cm per day during this timespan, assuming you round to 2 decimal places.

work shown:

compute f(3)

f(n) = 12*(1.03)^n

f(3) = 12*(1.03)^3

f(3) = 13.112724 < we'll use this later

compute f(10)

f(n) = 12*(1.03)^n

f(10) = 12*(1.03)^10

f(10) = 16.1269965521294 < we'll use this later

now use the formula below with a = 3 and b = 10

aroc = average rate of change

aroc = [ f(b) - f(a) ]/[ b - a ]

aroc = [ f(10) - f(3) ]/[ 10 - 3 ]

aroc = (16.1269965521294 - 13.112724)/(10 - 3)

aroc = 3.0142725521294/7

aroc = 0.43061036458991

round this however you need to

note: the plant grew approximately 3.01 cm over 7 days, so roughly 0.43 cm per day is the average growth rate (if you were to round to 2 decimal places).