.
This problem is to be solved MENTALLY.
The new computer works twice as productive as the old one.
So, the two computers together work as productive as three slower computer.
Thus you can re-formulate the problem EQUIVALENTLY saying that three slower computers make the job in 15 minutes.
Hence, one single slower computer makes the job in 3*15 = 45 minutes.
The newer computer, working two times faster that the older one, will complete the job in 45/2 = 22.5 minutes.
ANSWER. The newer computer will complete the job in 22 minutes and 30 seconds.
Solved.
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It is a standard and typical joint work problem.
There is a wide variety of similar solved joint-work problems with detailed explanations in this site. See the lessons
- Using Fractions to solve word problems on joint work
- Solving more complicated word problems on joint work
- Selected joint-work word problems from the archive
Read them and get be trained in solving joint-work problems.
Also, you have this free of charge online textbook in ALGEBRA-I in this site
- ALGEBRA-I - YOUR ONLINE TEXTBOOK.
The referred lessons are the part of this textbook under the topic
"Rate of work and joint work problems" of the section "Word problems".
Save the link to this online textbook together with its description
Free of charge online textbook in ALGEBRA-I
https://www.algebra.com/algebra/homework/quadratic/lessons/ALGEBRA-I-YOUR-ONLINE-TEXTBOOK.lesson
to your archive and use it when it is needed.