Answer: The required missing number is 10.
Step-by-step explanation: We are given to find the missing number in the following proportion :
[tex]?:14=15:21.[/tex]
Let the missing number be represented by x.
Then, according to the given information, we have
[tex]x:14=15:21\\\\\Rightarrow \dfrac{x}{14}=\dfrac{15}{21}\\\\\\\Rightarrow \dfrac{x}{14}=\dfrac{5}{7}\\\\\\\Rightarrow x=\dfrac{5}{7}\times14\\\\\Rightarrow x=10.[/tex]
Thus, the required missing number is 10.
