Four presses of ‘+’ take him four floors up; four presses of ‘–’ bring him four floors back down. The two movements cancel out completely.
Why: – 4 is the inverse of + 4. A number added to its inverse always gives 0.
Q2.
Write the inverses of these numbers: + 4, – 4, – 3, 0, + 2, – 1.
Answer
The inverse of a number is the number that brings you back to Floor 0. Keep the digits, change the sign.
Number
+ 4
– 4
– 3
0
+ 2
– 1
Inverse
– 4
+ 4
+ 3
0
– 2
+ 1
Check
4 + (– 4) = 0
– 4 + 4 = 0
– 3 + 3 = 0
0 + 0 = 0
2 + (– 2) = 0
– 1 + 1 = 0
Did you know? 0 is the only number that is its own inverse. Pressing the button zero times, and then zero times again, still leaves you on the ground floor.
Who is on the lowest floor? 1. Jay is in the Art Centre. So, he is on Floor + 2. 2. Asin is in the Sports Centre. So, she is on Floor ___. 3. Binnu is in the Cinema Centre. So, she is on Floor ___. 4. Aman is in the Toy Store. So, he is on Floor ___.
Answer
Child
Where
Floor
Jay
Art Centre
+ 2
Asin
Sports Centre
+ 5
Binnu
Cinema
– 3
Aman
Toy Store
– 1
Arrange the four floors the way they sit in the building:
+ 5 (Asin) > + 2 (Jay) > – 1 (Aman) > – 3 (Binnu)
Answer: Binnu is on the lowest floor — the Cinema, Floor – 3. Asin is on the highest.
Q5.
Should we write – 3 < – 4 or – 4 < – 3?
Answer
We should write – 4 < – 3 (and the same fact can be written as – 3 > – 4).
Look at the building: the Ghost House (Floor – 4) is below the Cinema (Floor – 3). Anything lower down is the smaller number.
Floor – 4 is lower than Floor – 3 → – 4 < – 3
Careful — a common mistake: with negative numbers, the one with the bigger digits is the smaller number. 4 > 3, but – 4 < – 3, because going down 4 floors takes you lower than going down 3 floors.