Worked Example 1
The temperature is minus 6 degrees at night and rises by 11 degrees by midday.
Set it upRising means moving right: −6 + 11
Count along the lineSix steps right reaches zero, and 5 of the 11 are left.
Answer5 degrees. The rise was bigger than the distance below zero, so the answer is positive.
Worked Example 2
An account is 2400 rupees overdrawn, and a debt of 900 rupees is cancelled.
Write it in symbols−2400 − (−900)
Two minus signs make a plus−2400 + 900 = −1500
Does it make sense?Still overdrawn, but by less than before, which is what cancelling part of a debt should do.
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