Subjects were classified according to which of three

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Solution:
It is asked to identify the IV, that is, independent variable and its scale of measurement.
Here, IV is praise for correct answers to math problems.
It is given that Group A received lots of praise, Group B received moderate praise and group C received no praise for correct answers to math problems.
That means, the data for praise has a natural order of a lot, moderate and absence.
So, the scale of measurement for IV is ordinal. There are 3 levels for the IV.
The DV is the dependent variable and in this case, it is the performance of subjects, that is, the scores in the posttest measure of mathematical ability and it is measured using Ratio scale of measurement since it has an absolute zero value and differences between the scores can be compared meaningfully.
The claim is: Does praise influence performance ?
The null and alternative hypotheses are:
${\displaystyle H_0}$: Praise does not influence performance. That means, praise and performance are independent of each other.
${\displaystyle H_1}$: Praise does influence performance. That means, praise and performance are dependent variables.