In a game A can give B 20 points in 60 and C 18 points in 90. How many points can C give B in a game of 120?
A can give C 18 points in 90
=> While A scores 90 points, C scores $\left(90-18\right)$=72 points
$\text{=> While A scores }\dfrac{90}{72}\text{ points, C scores 1 point.}$
$\text{=> While A scores }\dfrac{90}{72} \times 120 =\dfrac{90}{6} \times 10\text{ = 150 points, C scores 120 point.}$
A can give B 20 points in 60
=> While A scores 60 points, B scores $\left(60-20\right)$=40 points
$\text{=> While A scores 1 point, B scores }\dfrac{40}{60} = \dfrac{2}{3}\text{ points}$
$\text{=> While A scores 150 points, B scores }\dfrac{2}{3} \times 150 = 100\text{ points}$
i.e., while C scores 120 points, B scores 100 points
Hence, in a 120 race, C can give B $\left(120-100\right)$=20 points