(2) The number of people who don't often use calculators is:160-100-20 = 40;

The percentage of not using calculator is: 40÷ 160=25%,

The percentage of not using calculator is: 20 ÷ 160 = 12.5%.

Bar charts and fan charts are completed as follows:

(3)∵ The number of students using the "uncommon" calculator is 40, and the number of students randomly selected is 160.

Judging from the students in this survey, the probability that a student happens to be an "unusual" calculator is:

Answer: What is the probability that one of the students in this survey happens to be randomly "infrequently used"?

Test and analysis: (1) There are 100 people who know the commonly used calculators according to the bar chart, and 62.5% of them know the commonly used calculators from the fan chart, so we can get the solution:

100÷62.5%= 160。

(2) Subtract the number of people who use calculators and the number of people who don't use calculators from the sample size, find out the number of people who don't use calculators, and then calculate the percentage of each part to complete the histogram and fan chart.

(3) The probability that a student just draws an "infrequently used" calculator is that the number of students using the "infrequently used" calculator is divided by the number of students randomly selected.