When Bill and Bob got to Harry's house they found that he had finished the ladder. they took it out into the street. Now we will be able to climb into the bank, said Bob. It looks too thin to me, said Bill. Don't be stupid, said Bob. This is an invention. The Professor did the drawing. However, Bob did not know what the computer in the hat had done. When the computer heard Bob's voice, it know it was not the Professor. So it changed all the numbers round the wrong way. Instead of forty-two, the computer said twenty-four. It did the same with all the numbers. All the numbers on the drawing were wrong.