NCERT Solutions for Class 9 Maths Chapter 7 — Exercise Set 7.1#
Probability is measured on a scale from 0 (impossible) to 1 (certain):
| Label | Probability |
|---|---|
| Impossible | 0 |
| Less likely | between 0 and $\dfrac{1}{2}$ |
| Equally likely (even chance) | $\dfrac{1}{2}$ |
| More likely | between $\dfrac{1}{2}$ and 1 |
| Certain | 1 |
1. Rank the following events on a scale from 0 (Impossible) to 1 (Certain). Label each event: Impossible, less likely, equally likely (even chance), more likely, certain. Give reasons why you gave each event its ranking. #
(i) The next Monday will come after Sunday.
Certain — probability 1. Monday always follows Sunday; the order of the days of the week never changes.
(ii) It will snow in Mumbai in July.
Impossible — probability 0. Mumbai is a warm coastal city, and July is its monsoon season, with temperatures far above freezing. Snow needs freezing temperatures, so it does not happen there.
(iii) An elephant will walk through your classroom today.
Less likely — probability very close to 0. It is not strictly impossible (an elephant could be brought to a school), but it almost never happens, so it sits right at the bottom of the scale.
(iv) You will greet at least one friend at school tomorrow.
More likely — probability close to 1. On a normal school day you meet friends and greet them. It is not certain, because tomorrow could be a holiday or you or your friends could be absent.
Ranking from 0 to 1
Snow in Mumbai in July (0), an elephant in class (near 0), greeting a friend (near 1), Monday after Sunday (1).