A decimal place is wrong, just like looking at 10 and 1, or 1 and 0. 1. What is the difference? 10- 1=9， 1-0. 1=0.9。 This 45.72 must also be a multiple of 9. 45.72/9 = 5.08, that is, 50.8-5.08 = 45.72 yuan, and books are 45.72 yuan more. Was it 50.8 or 5.08? Think for yourself.

the second question

If we buy three more pens, we will consider it this way: divide the original pens into three equal parts, and buy one more pen for each part, 2 16/3 = 72 yuan. In this way, each pen is 1 yuan, and 72 yuan can buy more 1 pen, which is obviously 8×9 = 72. It turns out that 9 yuan and 72 yuan bought eight each, 26,544. After the price was 1 yuan, 8 yuan and 72 yuan bought 9 pieces each, 2 16 yuan bought 27 pieces, and 2 16/ 8 =27, and bought 3 more pieces.