Çözüldü Problem-Solving With A Two-Variable Linear Equation Set

The city library donated some children’s books to Mr. Clark’s first-grade class. If each student takes 4 books, there will be 20 books left. If 3 students do not take a book and the rest of the students take 5 books each, there will be no books left. How many books were donated to the class?

A) 120
B) 140
C) 160
D) 175
E) 185

https://dynamicpapers.com/wp-content/uploads/2019/12/Test-6.pdf
(Page 16, Section 2, Question 17)

Number of the Books That Were Donated: B
Number of The Students: S
B = S·4 + 20 ⇒ S = B / 4 - 5....(I)
B = (S - 3)·5 + 0....(II)
Substituting (I) in the equation (II) B = (B / 4 - 5 - 3)·5 ⇒ B / 4 = 40 ⇒ B = 160.

Another (Longer) Solution By Unnecessarily Finding Out The Number of The Students:
https://www.toppr.com/ask/question/...larks-firstgrade-class-if-each-student-takes/