RefactorTest.h

@interface RefactorTest : NSObject
@property (strong, nonatomic) NSMutableArray *arrayPayloadValue;

- (id) initWithArray:(NSArray *) thearray;

// this should return the sum of the array values
- (NSNumber *) sum;

// this should return the average of the array values
- (NSNumber *) average;

@end

RefactorTest.m

@implementation RefactorTest 

- (id) initWithArray:(NSArray *) thearray {
  self.arrayPayloadValue = [thearray mutableCopy];
  return self;
}

- (NSNumber *) sum {
  NSArray *tosum = [self.arrayPayloadValue copy];
  int *sum calloc(1,sizeof(int));
  NSNumber *endsum;
  for (NSNumber *i in tosum) {
    *sum = *sum + [i intValue];
  }
  return @(sum);
}

- (NSNumber *) average {
  NSAssert("This must be implemented");
}

@end