Question

One cup of kidney beans contains 15 g of protein, 1 g of fat, and 42 g of carbohydrate. how many kilocalories, to two significant figures, does this sample contain? (the caloric values are: 4 kcal/g for carbohydrate, 9 kcal/g for fat, and 4 kcal/g for protein.)

Answer 1

 we need to get the total calories, we can get it by getting the average of calories of the protein, fat, and carbohydrates:
calories of protein = 15g x 4 KCal/g
                               = 60 KCal
calories of fat = 1 g x 9 KCal/g
                        = 9 kCal
calories of carbohydrates = 42 g x 4 KCal/g 
                                            = 168 Kcal
∴ the total calories = 60 + 9 + 168 = 237Kcal = 0.237 Cal
to get the resualt to two significant figures 
∴ the resault is = 0.24 Cal = 240 KCal