The seconds hand

In your book, Maths Mela (Chapter 12), pairs of clocks show how long Rani, Raghav and Ritu take to do small jobs. We read the time from the seconds hand, the thin hand that moves fastest.

The seconds hand goes all the way round the clock in 60 seconds. There are 12 numbers on the clock, and 12 × 5 = 60, so the seconds hand takes 5 seconds to go from one number to the next. Moving 1 number is 5 seconds, 2 numbers is 10 seconds, 3 numbers is 15 seconds, and so on.

When Rani gets out of bed, the seconds hand moves from the 12 to the 6. That is 6 numbers: 6 × 5 = 30 seconds. When Raghav goes from his room to the kitchen, it moves from the 12 to the 7: 7 × 5 = 35 seconds. When Ritu picks up a piece of paper, it moves from the 9 to the 12: 3 numbers, so 15 seconds.

We can also go the other way and draw the seconds hand. If it starts at the 12 and Raghu takes 20 seconds to read a sentence, it moves 20 ÷ 5 = 4 numbers and stops at the 4. For 40 seconds it stops at the 8. For 60 seconds it goes one full round and is back at the 12.