Source: Manhattan Prep
The price of a phone call consists of a standard connection fee, which is constant, plus a per minute charge. A 10-minute call costs $2.90 and a 16-minute call costs $4.40. How much does a 13-minute call cost?
A. $3.55
B. $3.57
C. $3.58
D. $3.65
E. $3.77
The OA is D
The price of a phone call consists of a standard connection
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Hi All,
We're told that the price of a phone call consists of a standard connection fee, which is constant, plus a per minute charge, a 10-minute call costs $2.90 and a 16-minute call costs $4.40. We're asked for the cost of a 13-minute call. This question can be solved in a couple of different ways - and there's a great 'rate shortcut' that you can use to avoid some of the extra math that comes with certain approaches.
Since there's a standard connection fee, we know that the difference between the costs of two calls is solely due to the number of minutes in the call. With the given information (about a 10-minute call and a 16-minute call), the difference in price comes down to the 6 minute difference in the length of the calls. Thus, the extra 6 minutes cost an extra $4.40 - $2.90 = $1.50. We're asked for the cost of a 13-minute call - which is exactly 'halfway' between those two prices. Half of $1.50 is $0.75, so we can add that to the cost of a 10-minute call to find the cost of the 13-minute call. $2.90 + $0.75 = $3.65
Final Answer: D
GMAT assassins aren't born, they're made,
Rich
We're told that the price of a phone call consists of a standard connection fee, which is constant, plus a per minute charge, a 10-minute call costs $2.90 and a 16-minute call costs $4.40. We're asked for the cost of a 13-minute call. This question can be solved in a couple of different ways - and there's a great 'rate shortcut' that you can use to avoid some of the extra math that comes with certain approaches.
Since there's a standard connection fee, we know that the difference between the costs of two calls is solely due to the number of minutes in the call. With the given information (about a 10-minute call and a 16-minute call), the difference in price comes down to the 6 minute difference in the length of the calls. Thus, the extra 6 minutes cost an extra $4.40 - $2.90 = $1.50. We're asked for the cost of a 13-minute call - which is exactly 'halfway' between those two prices. Half of $1.50 is $0.75, so we can add that to the cost of a 10-minute call to find the cost of the 13-minute call. $2.90 + $0.75 = $3.65
Final Answer: D
GMAT assassins aren't born, they're made,
Rich
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Letting f = the standard connection fee and n = the per-minute charge, we can create two equations, one for the 10-minute call and one for the 16-minute call::BTGmoderatorLU wrote:Source: Manhattan Prep
The price of a phone call consists of a standard connection fee, which is constant, plus a per minute charge. A 10-minute call costs $2.90 and a 16-minute call costs $4.40. How much does a 13-minute call cost?
A. $3.55
B. $3.57
C. $3.58
D. $3.65
E. $3.77
f + 10n = 2.90
and
f + 16n = 4.40
Subtracting the first equation from the second, we have:
6n = 1.50
n = 0.25
Substituting 0.25 for n into the first equation, we see that f is:
f + 2.5 = 2.90
f = 0.4
So a 13-minute call costs 0.4 + 13 x 0.25 = $3.65.
Alternate solution:
If we let m = the per-minute charge, x = the number of minutes, b = the standard connection fee, and y = the total cost of an x-minute call, we will have y = mx + b. As we can see, this is a line, and the ordered pairs (10, 2.90) and (16, 4.40) are on this line. We are looking for the y-value when x = 13. We can observe that 13 is exactly halfway between 10 and 16; therefore, the y-value should be exactly halfway between 2.90 and 4.40 also. Thus y = (2.90 + 4.40)/2 = 7.30/2 = 3.65.
Answer: D
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$$? = f + 13c\,\,\,\,\left[ \$ \right]$$BTGmoderatorLU wrote:Source: Manhattan Prep
The price of a phone call consists of a standard connection fee, which is constant, plus a per minute charge. A 10-minute call costs $2.90 and a 16-minute call costs $4.40. How much does a 13-minute call cost?
A. $3.55
B. $3.57
C. $3.58
D. $3.65
E. $3.77
The constant fee (f) and the minute-charge (c) will be considered in CENTS. (Amounts in cents are always integers!)
$$\left\{ \matrix{
\,f + 10c = 290 \hfill \cr
\,f + 16c = 440 \hfill \cr} \right.\,\,\,\,\,\,\,\,\mathop \Rightarrow \limits^{\left( + \right)} \,\,\,\,\,\,2f + 26c = 290 + 440\,\,\,\,\,\,\mathop \Rightarrow \limits^{{\rm{focus}}\,!} \,\,\,\,\,\,? = {{2f + 26c} \over 2} = 145 + 220 = 365\,\,\,\,\,\,\left[ {\,{\rm{cents}}\,} \right]$$
This solution follows the notations and rationale taught in the GMATH method.
Regards,
Fabio.
Last edited by fskilnik@GMATH on Wed Oct 17, 2018 8:02 am, edited 1 time in total.
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A 10-minute call costs $2.90 and a 16-minute call costs $4.40BTGmoderatorLU wrote:Source: Manhattan Prep
The price of a phone call consists of a standard connection fee, which is constant, plus a per minute charge. A 10-minute call costs $2.90 and a 16-minute call costs $4.40. How much does a 13-minute call cost?
A. $3.55
B. $3.57
C. $3.58
D. $3.65
E. $3.77
The OA is D
$4.40 - $2.90 = $1.50, and 16 minutes - 10 minutes = 6 minutes
So, the extra $1.50 paid for extra 6 minutes of calling
So, $0.75 would pay for 3 minutes of calling
How much does a 13-minute call cost?
A 10-minute call costs $2.90
So, the cost of a 13-minute call = $2.90 + $0.75 = $3.65
Answer: D
Cheers,
Brent