NOTE: This assessment resource auto marks other derivations of the time format as correct (e.g., 08.45 and 8.45). However the correct formats for time should still be emphasised - especially the use of colons rather than decimal points.

Diagnostic and formative information:

Common errors that students can make with these questions are:

treating the minutes as decimal (base 10) rather than minutes (base 60);

not adding both the minutes and the hour component;

not carrying over the minutes to the hours as they make up 1 hour (recombining error).

Common response

Likely reason

Next steps

a) 8.45
b) 7.50
c) 8.30
d) 8.20

Students use a decimal point rather than colon.

About a third of students in the trial did this, and their answer was marked as "correct".

This can lead to confusion, as 7.50 could be interpreted as seven-and-a -half hours rather than 7 hours 50 minutes.

Students need to use the standard notation for writing time; for example write 8:45 rather than 8.45.

c) 7:90

Students may assumes there are 100 minutes in an hour.

Remind students that there are only 60 minutes in an hour.

Students need to rename 60 minutes as 1 hour.

d) 7:20

Calculates 7:10 + 10 minutes (rather than 1 hour and 10 minutes).

Get students to re-read the question carefully and check their answer.