SOLUTION: A student did a word-processing job for $48. It took him 8 hours longer than he expected, and therefore he earned $3 per hour less than he anticipated. How long did he expect that

Algebra ->  Rate-of-work-word-problems -> SOLUTION: A student did a word-processing job for $48. It took him 8 hours longer than he expected, and therefore he earned $3 per hour less than he anticipated. How long did he expect that       Log On


   



Question 1027022: A student did a word-processing job for $48. It took him 8 hours longer than he expected, and therefore he earned $3 per hour less than he anticipated. How long did he expect that it would take to do the job?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
I think the key to this problem is that the student
took the job for a FLAT RATE of $48.
If he was being paid hourly at a fixed HOURLY rate
and took longer, he would have made more, not less
---------------------------------------------
Let +t+ = time in hours he expected
it would take to do the job
+t+%2B+8+ = time in hours it actually
took him to do the job
Let +r+ = hourly rate in dollars he
expected to be paid for the job
+r+-+3+ = hourly rate in dollars that
he actually got paid for the job
-----------------------------------
Equation for what he expected would happen:
(1) +r%2At+=+48+
Equation for what actually happened:
(2) +%28+r+-+3+%29%2A%28+t+%2B+8+%29+=+48+
-------------------------
(2) +r%2At+-+3t+%2B+8r+-+24+=+48+
(2) +r%2A%28+t+%2B+8+%29+-+3t+=+72+
and
(1) +r+=+48%2Ft+
Substitute (1) into (2)
(2) +%2848%2Ft%29%2A%28+t+%2B+8+%29+-+3t+=+72+
(2) +48%2A%28+t+%2B+8+%29+-+3t%5E2+=+72t+
(2) +48t+%2B+384+-+3t%5E2+=+72t+
(2) +3t%5E2+%2B+24t+-+384+
(2) +t%5E2+%2B+8t+-+128+=+0+
I notice that +128+=+8%2A16+ and
+16+-+8+=+8+, so I can guess that:
(2) +%28+t+%2B+16+%29%2A%28+t+-+8+%29+=+0+
Time has to be positive, so +t+=+8+
He expected to finish the job in 8 hrs
---------------------------------
check:
(1) +r%2At+=+48+
(1) +r%2A8+=+48+
(1) +r+=+6+ dollars/hr
and
(2) +%28+r+-+3+%29%2A%28+t+%2B+8+%29+=+48+
(2) +%28+r+-+3+%29%2A%28+8+%2B+8+%29+=+48+
(2) +%28+r+-+3+%29%2A16+=+48+
(2) +r+-+3+=+3+
(2) +r+=+6+ dollars/hr
OK