Clock and Calendar Numbers

Class 6 Maths · Chapter 3: Number Play · NCERT Ganita Prakash section 3.7

Learn

Clock times can make patterns: 4:44, 10:10 and 12:21. A time like 12:21 reads the same both ways: it is a palindromic time.

Dates make patterns too. Ira was born on 20/02/2020: the pair 20 keeps coming back. Her cousin Tenzin was born on 12/02/2021, and 12022021 reads the same backwards: a palindrome date!

Rohan has the digits 5, 8, 1 and 6. The largest number he can make is 8651 and the smallest is 1568. Their difference is 7083 and their sum is 10,219.

8651 − 1568 = 7083 · 8651 + 1568 = 10,219

Explore: move the clock forward and look for palindromic times.

It is 4:50. Move the clock to the next palindromic time.
It is 7:58. Find the next palindromic time.
Use the tiles 5, 8, 1, 6 to make the largest number.

Remember

Palindromic times read the same both ways: 1:01, 4:44, 12:21.
Largest number: digits from big to small. Smallest: small to big (but not starting with 0).

Quick check

Which of these clock times is a palindrome?

10:01
10:10
12:12
9:45

Answer

10:01. 10:01 → 1001, which reads the same backwards.

Think about it

It is 3:33. What is the next palindromic time? How many palindromic times are there from 3:00 to 3:59?

One answer

The next one is 3:43, ten minutes later. From 3:00 to 3:59 there are six: 3:03, 3:13, 3:23, 3:33, 3:43 and 3:53.

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.