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NCERT Solutions for Class 5th Maths Chapter 12 (c) Minutes and seconds on a double number line — Let Us Do

Book page 1621 Updated on2026-09-19

Q1.
Fill in the blanks in the double number line to complete the conversions.
1 min60 sec___ min120 sec5 min___ sec10 min___ sec15 min___ sec___ min1200 sec___ min1500 sec× 60× 5
Page 162, Question 1 (c) — the double number line. Minutes on the top line, seconds on the bottom line.
Answer

Here is the completed line. Every minute on top is worth 60 seconds below.

minutes seconds 12 510 1520 25 60120 300600 9001200 1500
The 2 minute mark is written a little away from the 1 minute mark so the labels do not touch.
MinutesWorkingSeconds
1 min1 × 6060 sec
2 min2 × 60120 sec
5 min5 × 60300 sec
10 min10 × 60600 sec
15 min15 × 60900 sec
20 min1200 ÷ 601200 sec
25 min1500 ÷ 601500 sec
5 × 60 = 300    10 × 60 = 600    15 × 60 = 900
1200 ÷ 60 = 20    1500 ÷ 60 = 25
The same rule twice: Hours become minutes by × 60, and minutes become seconds by × 60 as well. Time is built in sixties all the way down. That is why the two double number lines on pages 161 and 162 look so alike.
A quick way to multiply by 60: multiply by 6, then put a zero at the end. 15 × 6 = 90, add a zero → 900. Try it on 25: 25 × 6 = 150, add a zero → 1500 ✓
Q1.
(i) 320 sec = ____ min ____ sec
Answer

5 minutes 20 seconds.

  1. Find the biggest whole minute inside 320 seconds. From the number line, 5 min = 300 sec. The next mark, 6 min, would be 360 sec — too big.
  2. Take out those 5 minutes: 320 − 300 = 20.
  3. So 320 seconds = 5 minutes 20 seconds.
320 ÷ 60 → 5 minutes, remainder 20
320 sec = 5 min 20 sec
Check it yourself: (5 × 60) + 20 = 300 + 20 = 320 ✓
Q1.
(ii) 225 sec = ____ min ____ sec
Answer

3 minutes 45 seconds.

  1. Count 60s: 60, 120, 180. The next one is 240, which is more than 225. So 3 whole minutes.
  2. Take them out: 225 − 180 = 45.
  3. So 225 seconds = 3 minutes 45 seconds.
225 ÷ 60 → 3 minutes, remainder 45
225 sec = 3 min 45 sec
Check it yourself: 180 + 45 = 225 ✓ That is about how long one over of cricket takes.
Q1.
(iii) 700 sec = ____ min ____ sec
Answer

11 minutes 40 seconds.

  1. Start from a mark you know. The number line says 10 min = 600 sec.
  2. How much is left? 700 − 600 = 100 seconds.
  3. 100 seconds is more than a minute, so take out one more minute: 100 − 60 = 40.
  4. Add up the minutes taken out: 10 + 1 = 11 minutes, with 40 seconds left.
700 − 600 = 100  (10 minutes taken out)
100 − 60 = 40  (1 more minute taken out)
700 sec = 11 min 40 sec
Check it yourself: (11 × 60) + 40 = 660 + 40 = 700 ✓
Q1.
(iv) 1,000 sec = ____ min ____ sec
Answer

16 minutes 40 seconds.

  1. Start from a mark you know. 15 min = 900 sec, from the number line.
  2. How much is left? 1000 − 900 = 100 seconds.
  3. Take out one more minute: 100 − 60 = 40.
  4. Total minutes: 15 + 1 = 16, with 40 seconds left over.
1000 − 900 = 100  (15 minutes taken out)
100 − 60 = 40  (1 more minute taken out)
1000 sec = 16 min 40 sec
Why 1000 seconds is not 16 and a half minutes: Half of 60 is 30, not 40. The leftover here is 40 seconds, which is two-thirds of a minute — a bit more than half.
Q1.
(v) 10 min 13 sec = ____ sec
Answer

613 seconds.

  1. Change the minutes into seconds: 10 × 60 = 600 seconds. The number line shows this directly.
  2. Add the loose seconds: 600 + 13 = 613.
10 min 13 sec
= (10 × 60) + 13
= 600 + 13
= 613 seconds
Q1.
(vi) 4 min 8 sec = ____ sec
Answer

248 seconds.

  1. Minutes into seconds: 4 × 60 = 240 seconds.
  2. Add the loose seconds: 240 + 8 = 248.
4 min 8 sec
= (4 × 60) + 8
= 240 + 8
= 248 seconds
Check it yourself: 248 − 240 = 8, and 240 ÷ 60 = 4 ✓
Q1.
(vii) 15 min 40 sec = ____ sec
Answer

940 seconds.

  1. Minutes into seconds: 15 × 60 = 900 seconds. Read it off the number line, or do 15 × 6 = 90 and add a zero.
  2. Add the loose seconds: 900 + 40 = 940.
15 min 40 sec
= (15 × 60) + 40
= 900 + 40
= 940 seconds
Did you notice? In (iii) we found 700 sec = 11 min 40 sec, and here 15 min 40 sec = 940 sec. The two questions are the same idea, just walked in opposite directions.
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