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Section 8: Program Branching and Controls 93

Examples

Example: Branching and Looping

A radiobiology lab wants to predict the

diminishing radioactivity of a test amount of

131

I, a radioisotope. Write a program to figure

the radioactivity at 3-day intervals until a

given limit is reached. The formula for N

, the

amount of radioisotope remaining after t days,

= N

-t/k

where k = 8 days, the half-life of

131

I, and N

is the initial amount.

The following program uses a loop to calculate the number of millicuries

(mci) of isotope theoretically remaining at 3-day intervals of decay.

Included is a conditional test to check the result and end the program when

radioactivity has fallen to a given value (a limit).

The program assumes t

 the first day of measurement  is stored in R

, N

 the initial amount of isotope  is stored in R

and the limit value for

radioactivity is stored in R

Keystrokes

Display

| ¥

000-

Program mode.

´ CLEAR M

000-

(Optional.)

´ b A

001-42,21,11

Each loop returns to this

line.

l 0

002- 45 0

Recalls current t which

changes with each loop.

´ ©

003- 42 31

Pauses to display t.

004- 8

005- 10

“

006- 16

–t/k.

007- 2

008- 34

009- 14

–t/k

1 2 ... 88 89 90 91 92 93 94 95 96 97 98 ... 287 288

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HP 15C Manuale Utente Pagina 93

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