Page 311 - Theory and Problems of BEGINNING CHEMISTRY

300 SCIENTIFIC CALCULATIONS [APP.

where the parentheses are required to signify that the addition and subtraction are to be done first. A calculator
has only one operation key for division, ÷ . When you use your calculator, be careful to indicate what is divided
by what when more than two variables are involved.

EXAMPLE A.14. Write the sequence of keystrokes required to perform each of the following calculations, where a, b,and
c represent numbers to be entered:
a + b
(a) (b) a + b/c + d (c) a + b/(c + d)
c + d

Ans. (a) ( a + b ) ÷ ( c + d ) = (c) a + b ÷ ( c + d ) =
(b) a + b ÷ c + d =

The Change-Sign Key
If we want to enter a negative number, the number is entered first, and then its sign is changed with the
change-sign +/− key, not the subtraction − key. The change-sign key changes the value on the display from
positive to negative or vice versa.

EXAMPLE A.15. Write the sequence of keystrokes required to calculate the product of 6 and −3.
Ans. 6 × 3 +/− =

The change-sign key converts 3 to −3 before the two numbers are multiplied.

EXAMPLE A.16. What result will be displayed after the following sequence of keystrokes?
7 +/− +/−
Ans. 7 (The first +/− changes the value to −7, and then the second +/− changes it back to +7.)

EXAMPLE A.17. (a) What result will be displayed after the following sequence of keystrokes?
3 +/− x 2 =
2
(b) What keystrokes are needed to calculate the value of −3 ?
2
Ans. (a) The +/− key changes 3 to −3 (minus 3). The squaring key x squares the quantity in the display (−3),
yielding +9.
2
(b) For the algebraic quantity −3 , the operations are done right to left; that is, the squaring is done first, and the
2
final answer is −9. To make the operations on the calculator follow the algebraic rules, enter 3 press x , and
then press +/−.

Exponential Numbers
When displaying a number in exponential notation, most calculators show the coefficient followed by a
space or a minus sign and then two digits giving the value of the exponent. For example, the following numbers
−3
3
represent 2.27 × 10 and 2.27 × 10 , respectively:
2.27 03
2.27− 03

Coefficient Exponent
Note that the base (10) is not shown explicitly on most calculators. If it is shown, interpreting the values of
numbers in exponential notation is slightly easier.
To enter a number in exponential form, press the keys corresponding to the coefficient, then press either
the EE key or the EXP key (you will have one or the other on your calculator), and finally press the keys