New A Level Histogram Question

So I'm doing Statistics and it's all good until I got this question:

To answer Part A I did the formula for frequency density (d=f/w where d is f. density, f is frequency and w is class width) to get that the frequency is 10 however the book says 5. Where have I gone wrong?

You are told that there are are 45 households so I'm guessing that you would assume that the total area is equal to 45? Try calculating the total area and see what you get. Please post your thoughts if you're still stuck after this.

Also, please try really hard to post your images the correct way up.

87 squares in total :/

That's not right plus you should be using the graph scales to find the area so the first bar would be 20 x 0.5.

You should know from GCSE that the area of a bar represents the total frequency for that class. All you're using here is f = fd x w.

So the area of the bar is the frequency?

It was at GCSE but it's slightly different at A Level because there may be scaling.

Try finding the total area (at GCSE this would be equal to the total frequency). This should hopefully show you what's happening here.