Priya's bus leaves the depot on time. Between stops it runs 3 minutes early, then 7 minutes late, then a further 2 minutes early, each change measured again...
Question 1 Report
Priya's bus leaves the depot on time. Between stops it runs 3 minutes early, then 7 minutes late, then a further 2 minutes early, each change measured against the timetable.
- Write down each change in Priya's journey as a directed number, treating early as negative. (2)
- Work out the bus's overall lateness or earliness when it reaches the final stop. (2)
Answer Details
This question tests writing directed numbers from a word description and combining them to find a net result.
(a) Running early is treated as negative and running late as positive, so the three changes in order are
\[-3, \; +7, \; -2\][2] (1 for the correct signs, 1 for all three values correct)
(b) Adding the three changes gives the overall lateness or earliness at the final stop:
\[-3 + 7 - 2 = 2\]Since the result is positive, the bus is \(2\) minutes late overall. [2] (1 for a correct running total, 1 for correctly stating the bus is 2 minutes late)
The sign of the final total tells you the direction of the overall result: here a positive total means late, but a negative total would have meant the bus was early overall.
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