This way might be more easier to understand for people but I could be wrong, I just want to know what people think....

- (IBAction)showFunFact {
    self.funFactLabel.text = [self.factBook.facts objectAtIndex:[Utility randomNumberBetween:0 max:self.factBook.numberOfObjectInArray]];

}

#import <Foundation/Foundation.h>

@interface FactBook : NSObject
@property (nonatomic, strong) NSArray *facts;
//Here i have added another property which will hold the number of objects in the array
@property (nonatomic) NSInteger numberOfObjectInArray;
-(NSString *) randomFact;
@end

- (instancetype)init
{
    self = [super init];
    if (self) {


        _facts = [[NSArray alloc] initWithObjects:
                  @"Ants stretch when they wake up.",
                  @"Ostriches can run faster than horses.",
                  @"Olympic gold medals are actually made mostly of silver.",
                  @"You are born with 300 bones; by the time you are an adult you will have 206.",
                  @"It takes about 8 minutes for light from the Sun to reach Earth.",
                  @"Some bamboo plants can grow almost a meter in just one day.",
                  @"The state of Florida is bigger than England.",
                  @"Some penguins can leap 2-3 meters out of the water.",
                  @"On average, it takes 66 days to form a new habit.",
                  @"Mammoths still walked the Earth when the Great Pyramid was being built.",
                  nil];

//Here i am setting the property to how many object there are in the array
        _numberOfObjectInArray = _facts.count;


    }
    return self;
}

@interface Utility : NSObject
+(NSInteger) randomNumberBetween:(NSInteger)min max:(NSInteger)max;
@end

@implementation Utility
+(NSInteger) randomNumberBetween:(NSInteger)min max:(NSInteger)max{

    return arc4random()%(max - min) + min;
}
@end