Answer: The value of the card after you buy your 8th coffee will be $61.3
Explanation:
The worth of the gift card for the coffee shop is $90. Each day you use the card to get a coffee for $4.10. This means that the worth of the gift card is reducing by $4.10 each day. This rate is in arithmetic progression.
The formula for the nth term of an arithmetic sequence, Tn is expressed as
Tn = a + (n-1)d
Where a is the first term
d is the common difference
n is the number of days
From the information given,
a = $90
d = - $4.1
The explicit formula representing the amount of money available will be
Tn = 90 - 4.1(n - 1)
The value of the card after you buy your 8th coffee will be
T8 = 90 - 4.1(8 - 1) = T8 = 90 - 4.1×7
T8 = 90 - 28.7
T8 = $61.3