Jina spends $20 dollars each time she travels toll roads. She started the month with $250 in her account, and so the amount of money she has left in her account after 1 trips is A(1) = 250 - 20t
a. How much money does she have left in her account after 4 trips? Show all work.
b. What is the largest number of trips she can take without running out of money in her account?

a) $170

b) 12

Step-by-step explanation:

A = 250 - 20t

where A is Jina's account balance and t is the number of trips she takes.

a)  If Jina takes 4 trips, then t = 4.  

Substitute t = 4 into the given equation:

A = 250 - (20 x 4)

  = 250 - 80

  = 170

So Jina has $170 left in her account after 4 trips.

b) The calculate the maximum number of trips Jina can take without running out of money, set A to zero and solve for t:

when A=0:                           0 = 250 - 20t

Add 20t to both sides:    20t = 250

Divide both sides by 20:     t = 12.5

Therefore, Jina can take 12.5 trips.  However, she can't take a half-trip so we should round the number down to 12 trips (as after 12 trips she will only have enough money left for half a trip).

So, the largest number of trips Jina can take without running out of money is 12.

answer: a

step-by-step explanation:

answer: c, the green line

step-by-step explanation:

there is no black line, eliminate b.

simple interest implies periodic payments, but the red line shows no payments, eliminate d.

simple interest has equal payments. if paid say every day, the graph is about a straight line (actually a stairstep).

the yellow line is not straight, eliminate a.

check: the green line is straight, answer is c.

simple interest with positive interest rate gives a straight line sloping up to the right. green line:

g(t) = $100 + ($200-$100) ÷ (20 years) × (t years)

= $100 + (4%/year) × ($100)(t years)

incidentally, the yellow line curving upward represents continuously compounded interest

y = $100 × 2^(t years / (14 assuming the yellow line hits $200 at 14 years. 2^0 is 1, so y(0) = $100; 2^(14/14) is 2, so y(14) = $200.