a. Calculate percentages like e.g. calculating the value added tax. [Prozente berechnen wie z.B. die Mehrwertsteuer ausrechnen.]

Nein

14 test persons stated that they could calculate percentages without any problems, four test persons could do so with certain difficulties and two test persons stated that they could do so only with great difficulties.

Two test persons asked the cognitive interviewer whether the calculation should be done in the head or with the help of a pocket calculator, whereby test person 06 (answer: with great difficulty) assumes mental arithmetic when answering and test person 20 (answer: I can do it without any problems) decides to use a pocket calculator as an aid when classifying their everyday mathematical competence.

With the help of the questionnaire it becomes clear that 14 test persons (TP 01, 04, 06, 07, 08, 09, 10, 11, 13, 15, 16, 17, 18, 19) thought of mental arithmetic when assessing their abilities, two test persons (TP 03, 20) thought of using a calculator or cell phone and four thought of both (TP 02, 05, 12, 14).

When asked whether they would have answered differently if they had thought about using a calculator, five of the 14 test persons who thought about mental arithmetic said that they could do this without any problems.

• "If I had to do it, I would already know how to do the math. But when I'm standing in the store, I have a hard time doing it." (TP 06, answer: with great difficulty)
• "If it is odd, it gets complicated, straight in the head. For example, if it's 27%, I need technical help.” (TP 07, answer: with certain difficulties)
• “At 50 %, 20 % or 10 % this is still possible, but as soon as 3 % of an odd number [should be calculated], it becomes more difficult. If I would calculate more often with a calculator and I would know how to do it in the calculator, it would be no problem. But I hardly ever do that.”(TP 10, answer: with great difficulties)
• "If you can write it down and calculate it with a calculator, then it works, but in your head like this.” (TP 12, answer: with certain difficulties)

Consequently, the variance of the scale results from the different ways in which technical aids are considered or not considered. In other words, those who claim to have some or great difficulties with the calculation of percentages, e.g. VAT, do so because they assume that the data should be calculated in their head. Only test person 05, who thinks of both mental arithmetic and the use of a calculator, sticks to her assessment that this task causes her certain difficulties: "I would have to think about it first and if I were to make a few mistakes, I would be fine. I would have to reach into certain areas of my brain that I otherwise never use. Nothing will change with a calculator, I think."

The variance in response behavior is largely due to the use of technical aids. Therefore, it should be specified whether only mental arithmetic or also the use of tools such as paper or calculators is allowed.

true