Page 318 - Theory and Problems of BEGINNING CHEMISTRY

APP.] SCIENTIFIC CALCULATIONS 307

A.20. If you have a value for the ratio x/y in the display of your calculator, what key(s) do you press to get the
value y/x?
Ans. The reciprocal key, 1/x

A.21. Perform the following calculations in your head. Check the results on your calculator:
(a)3+2×7 (b)3×2+7 (c)3×(2−7) (d)3×2/(5+1) (e)3×2/(4×1.5)
Ans. (a)17 (b)13 (c) −15 (d)1 (e)1

A.22. Perform the following calculations in your head. Check the results on your calculator:
(a)2 × (−6) (b)2 × 2 + (−6) (c) −4 × (2 − 6) (d) −3 × 7/(−4 − 3)

Ans. (a) −12 (b) −2 (c)16 (d) 3

A.23. What value will be obtained if 4 is entered on a calculator and then the change-sign +/− key is pressed
twice?

Ans. The answer is 4. The sign is changed to −4 the first time +/− is pressed, and −4 is changed back to 4 the
second time it is pressed.

2
A.24. What value will be obtained if 3 is entered on a calculator and then the square x key is pressed twice?
Ans. The answer is 81. The 3 is squared the first time x 2 is pressed, yielding 9 in the display. That 9 is squared
when x 2 is pressed again.

A.25. Write the exponential number corresponding to each of the following displays on a scientific calculator:
(a) 4.14 06 (b) 4.14−06 (c) −4.14 06 (d) −4.14−06 (e)1 07
Ans. (a)4.14 × 10 6 (b)4.14 × 10 −6 (c) −4.14 × 10 6 (d) −4.14 × 10 −6
(e)1 × 10 7

A.26. Write the display on a scientific calculator corresponding to each of the following exponential numbers:
(a)6.06 × 10 3 (b)6.06 × 10 −3 (c) −6.06 × 10 −3 (d) −3.03 × 10 −23
(e)1.7 × 10 −3
Ans. (a)6.06 03 (b)6.06 − 03 (c) −6.06 − 03 (d) −3.03−23 (e) 1.7 − 03

A.27. Put parentheses around two successive variables in each expression so that the value of the expression is
not changed. Use the precedence rules for algebra. For example, a × b + c is the same as (a × b) + c.
(a) a/b + c (c) a − b − c
(b) ab/c (d) a/bc
Ans. (a) (a/b) + c (c) (a − b) − c
(b) (ab)/c or a(b/c) (d) a/(bc)

A.28. Determine the value of each of the following expressions:
8
(782)(1/760)(1.40) (3.00 × 10 )(6.63 × 10 −34 )
(a) (c)
(0.0821)(273) 4.22 × 10 −10
2
(0.0821)(291) (1.40)(7.82 × 10 )/(7.60 × 10 )
2
(b) (d)
(0.909)(1.25) (8.21 × 10 )(2.73 × 10 )
2
−2
Ans. (a) 0.0643 (b) 21.0 (c) 4.71 × 10 −16 (d ) 0.0643
Note that part d and part a are the same except that part d is presented in scientific notation.