Jacob weighs 54 kilograms and 800 grams. Matthew weighs 53 kilograms and 400 grams. What is the difference, in grams, between their weights?
The phrase, what is the difference, gives us a clue how to find the answer to this problem. We’re given the weights of two children. Jacob weighs 54 kilograms and 800 grams. And we’re told that Matthew weighs 53 kilograms and 400 grams. The difference between these two weights is this distance here on our bar model. And so to find the difference between these two children’s weights, we can either subtract Matthew’s weight from Jacob’s or we can start with Matthew’s weight and count on until we get to Jacob’s. It doesn’t matter which of these methods we use. We’ll still find the same answer. So let’s use counting on.
So we’ll start with Matthew’s weight, 53 kilograms and 400 grams. If we add one kilogram to this, we have a total of 54 kilograms 400 grams. And so to get to Jacob’s weight of 54 kilograms 800 grams, we need to add another 400 grams. 400 plus 400 equals 800. So if we look at the jumps we’ve made, we can see the difference between the two children’s weights. We’ve jumped one kilogram 400 grams. But this isn’t quite the answer we need. We’re asked to give the difference in grams between their weights. A part of our answer is already in grams. Part of it needs to be converted.
How can we change one kilogram into grams. We can apply a fact we already know. One kilogram is the same as 1000 grams. So one kilogram 400 grams is the same as 1000 grams plus 400 grams. And if we add these together we get the total 1400 grams. If Jacob weighs 54 kilograms and 800 grams and Matthew weighs 53 kilograms and 400 grams, the difference between their weights is one kilogram 400 grams. We know that one kilogram is the same as 1000 grams. And so the difference between their weights in grams is 1400 grams. We’ve converted the mass from kilograms two grams to help us answer the problem.