.
In 3 days, Dimple made 
= 0.3 of the job; so, 1-0.3 = 0.7 of the job remained to be complete.
In 5 days, the two completed the job, so their combined rate of work was 
= 0.14.
The Dimple's individual rate of work is 
= 0.1 of the job per day.
Hence, the Chard's individual rate of work is the difference 0.14 - 0.1 = 0.04.
It means that Chard can do the entire job in 
= 25 days. ANSWER
Solved.
---------------
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.
===========
The major lessons to learn from my solution are THESE :
1) The problem can be solved mentally, without using equations,
manipulating with fractions, only.
2) An essential conception to use is the notion of rate of work.
3) When the combined rate of work is known and the rate of work of one participant is known, the rate of work
of the other participant is the difference of the rates.
Happy learning (!)
