Negative numbers · Usually met around P5
Differences across zero
Across 0: add the two parts.
How to do it
Method
Across 0: add the two parts
−3°C and 5°C are 3 + 5 = 8 degrees apart
Another way
Count the steps
−3 → 5: 8 steps
In full
How far apart two numbers are is how many steps lie between them on a number line. When one is below 0 and the other above, count in two parts: from −3 to 0 is 3 steps and from 0 to 5 is 5 steps, 3 + 5 = 8 in all. When both are negative, take their distances from 0 away from each other: −8 and −3 are 8 − 3 = 5 apart. A lift is the same: from B2 to floor 3 is 2 floors up to G and 3 more to floor 3, 5 floors. Or count the marks on a thermometer from the lower reading up to the higher one.
Worked examples
Have a go first, then open each one for the answer and the working.
Example 1
How many degrees apart are the temperatures on thermometers A and B?
Show the answer and working
Answer: 14 degrees
A shows 1°C and B -13°C: counting the marks from the lower up to the higher, they are 14 degrees apart.
Example 2
How many degrees apart are -8°C and -7°C?
Show the answer and working
Answer: 1 degrees
Both are below 0: take their distances from 0 away from each other, 8 and 7: 1 degrees.
Example 3
On a number line, how many steps apart are -2 and 1?
- A. 1
- B. 4
- C. 2
- D. 3
Choose the right answer
Show the answer and working
Answer: D. 3
-2 to 0 is 2 steps and 0 to 1 is 1: 2 + 1 = 3.
Practise it in the game →Negative numbers · Free to start, unlimited questions, no download