Chapter 8: Decimals (NCERT Solutions)
Exercise 8.1 (Tenths)
(a) Seven tenths (b) Two tens and nine tenths (c) Fourteen point six (d) One hundred and two ones (e) Six hundred point eight
(a) 0.7
(b) 20.9
(c) 14.6
(d) 102 (no decimal part; but written as 102.0)
(e) 600.8
(a) 19.4 (b) 0.3 (c) 10.6 (d) 205.9
| Number | Hundreds | Tens | Ones | Tenths |
|---|---|---|---|---|
| 19.4 | 0 | 1 | 9 | 4 |
| 0.3 | 0 | 0 | 0 | 3 |
| 10.6 | 0 | 1 | 0 | 6 |
| 205.9 | 2 | 0 | 5 | 9 |
(a) 5/10 (b) 3 + 7/10 (c) 200 + 60 + 5 + 1/10 (d) 70 + 8/10
(a) 5/10 = 0.5
(b) 3 + 7/10 = 3.7
(c) 200 + 60 + 5 + 1/10 = 265.1
(d) 70 + 8/10 = 70.8
(a) Eleven point two (b) Nine point five (c) Twelve point three seven
(a) 11.2
(b) 9.5
(c) 12.37
Exercise 8.2 (Hundredths)
| Hundreds | Tens | Ones | Tenths | Hundredths | Decimal |
|---|---|---|---|---|---|
| 0 | 0 | 3 | 2 | 5 | 3.25 |
| 1 | 0 | 2 | 6 | 3 | 102.63 |
| 0 | 3 | 0 | 0 | 5 | 30.05 |
(a) 5/100 (b) 15/100 (c) 27 + 6/100 (d) 9/100 (e) 4/10 + 8/100
(a) 5/100 = 0.05
(b) 15/100 = 0.15
(c) 27 + 6/100 = 27.06
(d) 9/100 = 0.09
(e) 4/10 + 8/100 = 40/100 + 8/100 = 48/100 = 0.48
Exercise 8.3 (Comparing Decimals)
(a) 0.3 or 0.4 (b) 0.07 or 0.02 (c) 3 or 0.8 (d) 0.5 or 0.05 (e) 1.23 or 1.2 (f) 0.099 or 0.19
(a) 0.4 (4 tenths > 3 tenths)
(b) 0.07 (7 hundredths > 2 hundredths)
(c) 3 (3.0 > 0.8)
(d) 0.5 (0.50 > 0.05)
(e) 1.23 (1.23 > 1.20)
(f) 0.19 (0.190 > 0.099)
(i) 0.8 > 0.08 (ii) 1.01 > 0.99 (iii) 0.5 > 0.49 (iv) 3.5 > 3.05 (v) 10.1 > 9.9
(a) 0.4, 0.57, 0.29 (b) 0.10, 0.081, 0.009 (c) 1.1, 2.1, 0.111 (d) 2.2, 2.02, 2.222, 2.22
(a) 0.29, 0.4, 0.57
(b) 0.009, 0.081, 0.10
(c) 0.111, 1.1, 2.1
(d) 2.02, 2.2, 2.22, 2.222
Exercise 8.4 (Fractions as Decimals)
(a) 5 paise (b) 75 paise (c) 20 paise (d) 50 rupees 90 paise (e) 725 paise
(a) 5 paise = 5/100 rupees = Rs. 0.05
(b) 75 paise = 75/100 = Rs. 0.75
(c) 20 paise = Rs. 0.20
(d) 50 rupees 90 paise = Rs. 50.90
(e) 725 paise = 700 paise + 25 paise = 7 rupees 25 paise = Rs. 7.25
(a) 15 cm (b) 6 cm (c) 2 m 45 cm (d) 9 m 7 cm (e) 419 cm
(a) 15 cm = 15/100 m = 0.15 m
(b) 6 cm = 0.06 m
(c) 2 m 45 cm = 2.45 m
(d) 9 m 7 cm = 9.07 m
(e) 419 cm = 400 cm + 19 cm = 4 m + 0.19 m = 4.19 m
(a) 8 m (b) 88 m (c) 8888 m (d) 70 km 5 m
(a) 8 m = 8/1000 km = 0.008 km
(b) 88 m = 0.088 km
(c) 8888 m = 8 km + 888 m = 8.888 km
(d) 70 km 5 m = 70.005 km
(a) 2 g (b) 100 g (c) 3750 g (d) 5 kg 8 g (e) 26 kg 50 g
(a) 2 g = 2/1000 kg = 0.002 kg
(b) 100 g = 100/1000 = 0.100 kg
(c) 3750 g = 3 kg + 750 g = 3.750 kg
(d) 5 kg 8 g = 5.008 kg
(e) 26 kg 50 g = 26.050 kg
Exercise 8.5 (Addition of Decimals)
(a) 0.007 + 8.5 + 30.08 (b) 15 + 0.632 + 13.8 (c) 27.076 + 0.55 + 0.004
(d) 25.65 + 9.005 + 3.7 (e) 0.75 + 10.425 + 2 (f) 280.69 + 25.2 + 38
(a) 0.007 + 8.500 + 30.080 = 38.587
(b) 15.000 + 0.632 + 13.800 = 29.432
(c) 27.076 + 0.550 + 0.004 = 27.630
(d) 25.650 + 9.005 + 3.700 = 38.355
(e) 0.750 + 10.425 + 2.000 = 13.175
(f) 280.690 + 25.200 + 38.000 = 343.890
Total = 35.75 + 32.60 = Rs. 68.35.
Total = 10.50 + 15.80 = Rs. 26.30.
Exercise 8.6 (Subtraction of Decimals)
(a) 18.3 − 11.7 (b) 20.05 − 9.3 (c) 24 − 0.023 (d) 16.508 − 5.91 (e) 4.2 − 3.72
(a) 18.30 − 11.70 = 6.60
(b) 20.05 − 9.30 = 10.75
(c) 24.000 − 0.023 = 23.977
(d) 16.508 − 5.910 = 10.598
(e) 4.20 − 3.72 = 0.48
Change = 50.00 − 35.65 = Rs. 14.35.
Amount spent = 11.25 + 3.30 = 14.55.
Amount left = 18.50 − 14.55 = Rs. 3.95.
20 m 5 cm = 20.05 m. 4 m 50 cm = 4.50 m.
Remaining = 20.05 − 4.50 = 15.55 m (15 m 55 cm).
Chapter 8: Decimals (Practice Questions)
RD Sharma / HOT Practice
4 → Tens place = 40
7 → Ones place = 7
8 → Tenths place = 0.8
3 → Hundredths place = 0.03
9 → Thousandths place = 0.009
3/4 = 75/100 = 0.75.
5 and 3/4 = 5.75.
All have same ones digit (7). Compare decimal parts:
7.330 > 7.30 > 7.03 > 7.003.
Descending: 7.330, 7.30, 7.03, 7.003.
350 g = 350/1000 kg = 0.350 kg.
Total = 8.350 kg.
7.500 + 8.346 + 12.090 + 6.007 = 33.943.
100.500 − 47.638 = 52.862.
1.250 + 0.875 + 1.400 = 3.525 km.
Total spent = 85.50 + 63.75 = 149.25.
Left = 250.00 − 149.25 = Rs. 100.75.
32.5 is greater.
Difference = 32.50 − 3.25 = 29.25.
75 m = 75/1000 km = 0.075 km.
Total = 3.075 km.
Required decimal = 8.05 − 1.90 = 6.15.
2.075 = 2075/1000.
HCF(2075, 1000) = 25.
2075/1000 = 83/40 = 83/40 (or 2 and 3/40).
4 pens = 4 × 3.75 = Rs. 15.00.
3 pencils = 3 × 1.25 = Rs. 3.75.
Total = 15.00 + 3.75 = Rs. 18.75.
0.875 = 875/1000. HCF(875, 1000) = 125.
875/1000 = 7/8.
3.7 = 3 + 7/10 = 37/10.
4.7 lies between 4 and 5.
4.7 is closer to 5 (since 0.7 > 0.5, so it is more than halfway to 5).
0.0050 has 4 decimal places. It is equal to 0.005 (trailing zeros after the last significant digit do not change the value). Yes, 0.0050 = 0.005.
Total cut = 4.75 + 6.50 = 11.25 m.
Remaining = 18.6 − 11.25 = 7.35 m.
2.500 + 3.250 + 1.075 = 6.825 kg.
5.60 + 3.47 = 9.07.
9.07 − 2.90 = 6.17.
6.17 + 0.08 = 6.25.
Chapter 8: Decimals (Concepts & Summary)
1. Decimal Place Value Chart
| Thousands | Hundreds | Tens | Ones | • (Decimal point) | Tenths | Hundredths | Thousandths |
|---|---|---|---|---|---|---|---|
| 1000 | 100 | 10 | 1 | 1/10 | 1/100 | 1/1000 |
Example: In 24.756 → 2 (tens), 4 (ones), 7 (tenths), 5 (hundredths), 6 (thousandths).
2. Comparing Decimals
- Compare the whole number parts first. The one with the larger whole number is greater.
- If whole parts are equal, compare the tenths digits first.
- If tenths are also equal, compare hundredths, then thousandths.
Tip: Add trailing zeros to make decimal places equal for easier comparison.
e.g., 0.3 = 0.300 and 0.29 = 0.290 → 0.300 > 0.290.
3. Fractions ↔ Decimals (Measurement Conversions)
| Conversion | Rule | Example |
|---|---|---|
| Paise → Rupees | Divide by 100 | 75 p = Rs. 0.75 |
| cm → m | Divide by 100 | 45 cm = 0.45 m |
| m → km | Divide by 1000 | 350 m = 0.350 km |
| g → kg | Divide by 1000 | 750 g = 0.750 kg |
| ml → litres | Divide by 1000 | 250 ml = 0.250 L |
4. Addition & Subtraction of Decimals
- Write the decimals in a column with decimal points aligned vertically.
- Fill in the missing decimal places with zeros.
- Add or subtract as with whole numbers, keeping the decimal point in the same position in the answer.
Example (Addition): 12.5 + 6.37
12.50
+ 6.37
─────
18.87
Example (Subtraction): 20.00 − 7.45 = 12.55
5. Key Points to Remember
- Trailing zeros after the last digit after the decimal point do not change the value: 2.50 = 2.5.
- Leading zeros before the first significant digit matter: 0.05 ≠ 0.5.
- To convert a fraction with denominator 10 or 100 to decimal: e.g., 3/10 = 0.3, 27/100 = 0.27.
- A decimal number is between two consecutive whole numbers. e.g., 4.7 is between 4 and 5.
- Every fraction can be written as a decimal and every decimal as a fraction.
