How can you use a bar diagram to check the accuracy of the solution to a ratio or rate problem?

You could potentially use a composite bar graph to show a ratio. Alternatively, if you have a total, say $5, shared out in the ratio 2:3, you could see if 2 of the 5 parts were represented by the 2 bar and 3 parts by the 3 bar by checking the scale on the y axis.