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6. a cell phone company offers a contract for which the cost C, in dollars, of t minutes of telephoning?
is given by C=0.25(t-400)+47.95, where it is assumed that t>=400 minutes. What times will keep costs between $86.20 and $114.95?
23. solve and grapgh the compound inequity
2x-14<=-7 or x-6>=1
the solution of the compound inequality is {x|x<=__ or x>=__}?.
3 Answers
- Jun AgrudaLv 71 decade agoFavorite Answer
0.25(t - 400) + 47.95 = 86.20
0.25(t - 400) = 38.25
t - 400 = 153
t = 553
0.25(t - 400) + 47.95 = 114.95
0.25(t - 400) = 67
t - 400 = 268
t = 668
Answer: 553 ≤ t ≤ 668 or Between 553 and 668
-----------
2x - 14 ≤ - 7
2x ≤ 7
x ≤ 7/2 or 7/2 ≥ x
x - 6 ≥ 1
x ≥ 7
Answer: 7/2 ≥ x ≥ 7???????
- peabodyLv 71 decade ago
C=0.25(t-400)+47.95
86.20 = 0.25(t-400)+47.95
(86.20 - 47.95)/.25 = t - 400
t = (86.20 - 47.95)/.25 + 400
= 553 mins
114.95 = 0.25(t-400)+47.95
(114.95 - 47.95)/.25 = t -400
t = (114.95 - 47.95)/.25 + 400
= 668 mins
23) 2x -14 <= -7
2x<= -7 +14
2x <- 7
x <- 7/2
x -6 >= 1
x >= 7
{x|x<= -7/2 or x>= 7}
Graph the compound inequality gives two regions to the left an equal to -7/2 and to the right or equal
to 7.
- 1 decade ago
For the first one, just set C = to the wanted costs:
86.20 = 0.25(t-400)+47.95 and 114.95 = 0.25(t-400)+47.95
and solve for t. Give the answer like this: (minutes for first part) <= t <= (minutes for last part). I'll let you put it in the calculator!
For the second one,
2x - 14 <= -7
2x <= -21
x<= -21/2
x- 6 >= 1
x >= 7
Therefore, {x|x<= -21/2 or x>= 7}
