How to put variable inside string-resources?

Just pass it throught getString() function as formatArgs Object.

int nextResultsSize = getNextResultsSize();
String strNextResultsSize = 
     getResources().getString(R.string.next_x_results, nextResultsSize);

XML:

<string name="next_x_results">Next %1$d results</string>

<string name="meatShootingMessage">You shot %1$d pounds of meat!</string>  


int numPoundsMeat = 123;
String strMeatFormat = getResources().getString(R.string.meatShootingMessage, numPoundsMeat);

Example taken from here

<string name="message">You shot %1$d pounds of meat! Put Second Variable String here %2$s and third variable integer here %3$d</string>
int intVariable1 = 123;
String stringVariable2 = "your String";
int intVariable3 = 456;
String strMeatFormat = getResources().getString(R.string.message, intVariable1, stringVariable2 , intVaribale3);