Hinglish

A Building of Fun

Class 6 Maths · Chapter 10: The Other Side of Zero · NCERT Ganita Prakash section 10.1

Learn

Sahil's city has a new Funhouse Tower. Above the ground are floors +1 to +7: a science corner, a toy shop, a food court and more. Below the ground are floors −1 to −4: parking, a bowling alley, a snow room and a mirror maze. The entrance is on the ground, floor 0.

Floors above the ground get positive numbers (+1, +2, …). Floors below get negative numbers (−1, −2, …), read as "minus one", "minus two". Zero is neither positive nor negative. Together, …, −3, −2, −1, 0, +1, +2, +3, … are called integers.

The lift has buttons that show a movement, not a floor: +3 means go up 3 floors, −2 means go down 2 floors. Nisha is on floor −2 and presses +5: she reaches floor +3. We write (−2) + (+5) = +3.

start + movement = target · (−2) + (+5) = +3

Going the other way: Farhan is at the book café (+4) and wants the snow room (−3). Which button? He must go down 7 floors: −7. Movement = target − start: (−3) − (+4) = −7.

target − start = movement · (−3) − (+4) = −7

A higher floor has a greater number. So −1 > −4 (the parking is above the mirror maze), and every positive number is greater than every negative number. On a number line lying flat, greater numbers are to the right.

Explore: ride the lift.

  1. Go to the snow room, floor −3.
  2. You are on +2. Make the movement −5. Which floor do you reach?
  3. You are in the mirror maze (−4). Go to the food court (+3). What movement was that?

Remember

  • Integers: …, −3, −2, −1, 0, +1, +2, +3, … Negative numbers are below (or left of) zero.
  • start + movement = target; target − start = movement.

Quick check

The lift is on floor −1. Gauri presses −3. Where does it stop?

  1. −4
  2. +2
  3. −2
  4. +4
Answer

−4. Down 3 floors from −1: −2, −3, −4. So (−1) + (−3) = −4.

Think about it

From floor +2, Divit presses +3, then −6, then +4. Where does he end up? Is there one button that would have done the same?

One answer

+2 + 3 = +5, then +5 − 6 = −1, then −1 + 4 = +3. The three movements add up to +3 − 6 + 4 = +1, so pressing +1 once does the same.

Practice

Practise with fresh questions at three levels (easy, medium, hard), some answered hands-on, with hints and worked answers. Get 4 of your last 5 right to finish the topic.