NCERT Solutions Ganita Prakash Chapter 10 Using the unmarked number line to add and subtract — In-text Question
Book page 255 Updated on2026-09-05
Q1.
Use unmarked number lines to evaluate these expressions: a. – 125 + (– 30) b. + 105 – (– 55) c. + 80 – (– 150) d. – 99 – (– 200)
Answer
On an unmarked number line (UNL) only 0 is shown. Mark the starting number roughly in the right place, draw the jump, and read the answer.
Start at – 125 and jump 30 further backwards — you land on – 155.Subtraction asks for the movement from – 55 to + 105: 55 steps to reach 0 and 105 more, that is + 160 in all.
a. – 125 + (– 30) = – 155
b. + 105 – (– 55) = 105 + 55 = + 160
c. + 80 – (– 150) = 80 + 150 = + 230 (from – 150 up to 0 is 150, then 80 more)
d. – 99 – (– 200) = – 99 + 200 = + 101 (from – 200 up to – 99 is 101 steps)
Tip: The unmarked number line does not need a scale. All it has to show is which side of 0 each number is on and which is further from 0.