Page 53 - TB_6B

21 Positive Signs and Negative Signs

A car moves from west to east at the speed of 2 km per minute.
The car is at 0 km now. Find the positions of the car at different times.

2 minutes 1 minute Present: 1 minute 2 minutes
ago: 4 km ago: 2 km 0 km later: 2 km later: 4 km

3 km 1 km 1 km 3 km

The present time is also 0. Use to indicate the time in the future and
to indicate the time in the past. Multiply the numbers to show the car’s

position at different times.

Time Distance Car Can Travel ( Time Car’s Position
in 1 Minute(km) : later, : ago)

Future 2 2 2 2=4 2
2 1 2 1=2 2
2
Present (0) 2 0 2 0=0 2

Past 2 1 2 1= 2
2 2 2 2= 4

Find the positions of the car 10 minutes before now and 10 minutes later
from now.

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