Answer: The number of red marbles in the jar is 48.
Step-by-step explanation: Given that the number of white, black and red marbles in a jar are in the ratio 5 : 11 : 18. And the total number of marbles in the jar is 144.
We are to find the number of red marbles in the jar.
Let, 5x, 11x and 8x be the number of white, black and red marbles in the jar.
Then, according to the given information, we have
![5x+11x+8x=144\\\\\Rightarrow 24x=144\\\\\Rightarrow x=6.](https://img.qammunity.org/2020/formulas/mathematics/middle-school/pe6udk4plhjbpt3ch4wrxhpxmd38e0ln9n.png)
Therefore, the number of red marbles will be
![8x=8*6=48.](https://img.qammunity.org/2020/formulas/mathematics/middle-school/ljbnop5jsxrjorsd9rlpzvlca0aiq8n4cj.png)
Thus, there are 48 red marbles in the jar.