19
Ti36eng1.doc TI-36X II Manual Linda Bower Revised:
01/10/03 10:47 AM Printed: 01/10/03 10:47 AM Page 19 of
48
³
Problem
A radioactive substance decays exponentially. If y
o
grams of certain radioactive substance are initially
present, the number of grams y(t) after t days is given
by the formula:
y(t)=y
o
e
-0.00015t
After 340 days, how much of a 5-gram sample of this
radioactive substance remains? After 475 days? Store
the constant part of the exponent to memory so you
need enter it only once. Round results to two decimal
places.
J
0
I
0 0 0 1 5
S V
L
0.00015
Þ
A
ß
L
0.00015
DEG
5
< % d " " " V
R <
3 4 0
O V
5
è
e^(A
è
340)
ß
4.751393353
DEG
% t
2
5
è
e^(A
è
340)
ß
4.75
FIX
DEG
5
< % d " " " V
R <
4 7 5
O V
5
è
e^(A
è
475)
ß
4.66
FIX
DEG
About 4.75 grams of this radioactive substance remain
after 340 days, and 4.66 grams remain after 475 days.
