Cesium-137 Decay- Medicine C esiu m -137 is a radioisotope u sed in radiology w here levels
are m easu red in m illicuries (mci). Use th e graph at th e right. W hat is
a reasonable estim ate of th e half-life of ce siu m -137?
U
£Challenge 41. Credit Suppose you use a credit card to buy a new suit for $250. If £
you do n o t pay th e entire balance after one m onth, you are charged
1.8% m onthly interest on your acco u n t balance. Suppose you can
m ake a $30 paym ent each m onth.
a. W hat is your balance after your first m onthly paym ent?
b. How m u ch interest are you charged on th e rem aining balance after your
first paym ent?
c. W hat is your balance ju st before you m ake your second
payment?
d. W hat is your balance after your seco n d paym ent?
e. How m any m o n th s will it take for you to pay off th e entire bill?
f. How m u ch interest will you have p aid in all?- Open-Ended Write two exponential growth functions / ( x ) an d g(x) such th at
f{x) < g(x) for x < 3 an d /( x ) > g(x) for x > 3.
Apply What You've Learned
Use the c o m p o u n d interest form ula A = 1 + a n d th e inform ation
on page 417 ab o u t the two CDs th a t Emilio is considering. Select all of the
following th at are true. Explain your reasoning.
A. The c o m p o u n d interest form ula is an exponential grow th function.
B. The c o m p o u n d interest form ula is an exponential decay function.
C. For th e CD from Bank West, n = 12.
D. For th e CD from First Bank, nt = 60.E. The grow th/decay factor for th e CD from Bank West is 11 + 0,838 j~4.F. The grow th/decay factor for th e CD from Bank West is 1 1 + ^
G. The g row th/decay factor for th e CD from First Bank is 0.00316.MAIHEMAIICAL
PRACTICES
MP4J466 Ch ap t er 7 Ex p o n e n t s a n d Ex p o n e n t i a l Fu n c t i o n s
20 40 60
Time (yr)