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NCERT Solutions Ganita Prakash Chapter 10 Addition to keep track of movement — Figure it Out

Book page 245 Updated on2026-09-05

Q1.
You start from Floor + 2 and press – 3 in the lift. Where will you reach? Write an expression for this movement.
Answer

Floor + 2 is the Art Centre. Pressing – 3 takes you three floors down: + 2 → + 1 → 0 → – 1.

Starting Floor + Movement = Target Floor
(+ 2) + (– 3) = – 1

Answer: Floor – 1 — the Toy Store.

Why the answer is negative: you go down 3 floors but you were only 2 floors above the ground, so you end up 1 floor below the ground.
Q2.
Evaluate these expressions (you may think of them as Starting Floor + Movement by referring to the Building of Fun). a. (+ 1) + (+ 4) b. (+ 4) + (+ 1) c. (+ 4) + (– 3) d. (– 1) + (+ 2) e. (– 1) + (+ 1) f. 0 + (+ 2) g. 0 + (– 2)
Answer
ExpressionJourney in the liftAnswer
a.(+ 1) + (+ 4)From Food Court go 4 floors up+ 5
b.(+ 4) + (+ 1)From Ice Cream go 1 floor up+ 5
c.(+ 4) + (– 3)From Ice Cream go 3 floors down+ 1
d.(– 1) + (+ 2)From Toy Store go 2 floors up+ 1
e.(– 1) + (+ 1)From Toy Store go 1 floor up0
f.0 + (+ 2)From Welcome Hall go 2 floors up+ 2
g.0 + (– 2)From Welcome Hall go 2 floors down– 2
Two things worth noticing: parts (a) and (b) give the same answer — the order of adding does not matter. In part (e) the two numbers are inverses of each other, so you land back on the ground floor, 0.
Q3.
Starting from different floors, find the movements required to reach Floor – 5. For example, if I start at Floor + 2, I must press – 7 to reach Floor – 5. The expression is (+ 2) + (– 7) = – 5. Find more such starting positions and the movements needed to reach Floor – 5 and write the expressions.
Answer

Use Movement = Target Floor – Starting Floor with Target Floor = – 5 every time.

Starting FloorButton press neededExpression
+ 6 (Space)– 11(+ 6) + (– 11) = – 5
+ 5 (Sports Centre)– 10(+ 5) + (– 10) = – 5
+ 3 (Book Store)– 8(+ 3) + (– 8) = – 5
+ 1 (Food Court)– 6(+ 1) + (– 6) = – 5
0 (Welcome Hall)– 50 + (– 5) = – 5
– 2 (Video Games)– 3(– 2) + (– 3) = – 5
– 4 (Ghost House)– 1(– 4) + (– 1) = – 5
– 5 (Dinosaur)0(– 5) + 0 = – 5
Why every press is ‘–’ (or 0): Floor – 5 is the lowest floor of the building, so from anywhere else you can only come down to it. If you are already there, you press nothing — a movement of 0.
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