The student makes small counting errors. If the answer is too small, they may have omitted to count one coin (or even a note).

The student could recount the money. If they still cannot get it correct, they may do the task from a printed version, ticking each coin or note off as they go.

a)

b)

c)

23 or 23.0
9.6
17.2

The student gets the correct answer, but does not write it in the standard way for dollars and cents.

The student could look at the way amounts of money are written in advertisements in newspapers or junk mail. See if they notice that there are always two figures after the decimal point (i.e., for the cents).