How to get the first value from NSMutableArray (iPhone)?

It seems you have an array of arrays, so this will be:

[[myArray objectAtIndex:0] objectAtIndex:0];

Or using a subscription:

myArray[0][0];

Edit

Ok, you have an array NSStrings. To do what you want (get 53.399), follow these steps:

NSString *myString = [myArray objectAtIndex:0];
NSArray *stringComponents = [myString componentsSeparatedByString:@","];
NSString *myFinalString = [stringComponents objectAtIndex:0];

With signature:

NSString *myFinalString = [[myArray[0] componentsSeparatedByString:@","][0];