Try this beautiful problem from the Pre-RMO, 2017 based on ratio.
Problem on Ratio – PRMO 2017
In a sports team, the total number of boys and girls are in the ratio 4:3. On one day it was found that 8 boys and 14 girls were absent from the team and that the number of boys was the square of the number of girls, find the total number of members in the sports team.
- is 107
- is 42
- is 840
- cannot be determined from the given information
Key Concepts
Ratio
Integers
Algebra
Check the Answer
But try the problem first…
Answer: is 42.
PRMO, 2017, Question 12
Elementary Algebra by Hall and Knight
Try with Hints
First hint
here ratio = 4:3
\(\Rightarrow boys =4x, girls=3x\)
given \((4x-8)=(3x-14)^{2}\)
Second Hint
\(\Rightarrow 4x-8=9x^{2}-84x+196\)
\(\Rightarrow 9x^{2}+196-84x=4x-8\)
\(\Rightarrow 9x^{2}-88x+204=0\)
Final Step
\(x=\frac{88\pm\sqrt{88^{2}-4(9)(204)}}{18}\)
\(\Rightarrow x=6 or \frac{34}{9}\)
\(\Rightarrow 7x=42\) or non-integer
\(\Rightarrow 42 members.\)
Other useful links
- https://www.cheenta.com/rational-number-and-integer-prmo-2019-question-9/
- https://www.youtube.com/watch?v=lBPFR9xequA
Related Program
Math Olympiad Program… taught by Olympians and researchers