Page 53 - Start Up Mathematics_7

7 45
Solution: (a) 7 cm = m = 0.07 m (b) 45 mm = cm = 4.5 cm
100 10
0.07 4.5
= km = m = 0.045 m
1,000 100
0.045
= 0.00007 km = 1,000 km = 0.000045 km
Example 6: Express in kg:
(a) 3,470 g (b) 12 kg 8 g (c) 2,598 mg
, 3 470
Solution: (a) 3,470 g = kg = 3.470 kg
, 1 000
8
(b) 12 kg 8 g = 12 kg + kg = 12.008 kg
1,000
2,598 2.598
(c) 2,598 mg = g = 2.598 g = kg = 0.002598 kg
1,000 1,000

Addition and Subtraction of Decimals
Following steps are used for addition and subtraction of decimals:
Step 1: Convert the given decimals to be added or subtracted to like decimals.

Step 2: Write decimal numbers one below the other in such a way that the decimal point of each
number is exactly below the number above.
Step 3: Now add or subtract as we do in whole numbers.

Step 4: Place the decimal point in the answer directly below the other decimal points.
Example 7: Shantanu went from place A to place B and from 8.5 km B
there to place C. A is 8.5 km from B and B is A
12.7 km from C. Gulzar went from place A 12.7 km
to place D and from there to place C. D is 9.1 km
9.1 km from A and C is 11.8 km from D. Who C
travelled more and by how much? D 11.8 km
Solution: Shantanu travelled from A to B and B to C, i.e., AB + BC
= 8.5 km + 12.7 km = 21.2 km

Gulzar travelled from A to D and D to C, i.e., AD + DC
= 9.1 km + 11.8 km = 20.9 km
Clearly, Shantanu travelled more by = (21.2 – 20.9) km = 0.3 km.

Example 8: Shyama bought 5 kg 300 g apples and 3 kg 250 g mangoes. Sarla bought 4 kg 800 g
oranges and 4 kg 150 g bananas. Who bought more fruits? (NCERT)

300
Solution: Apples bought by Shyama = 5 kg 300 g = d5 + nkg = 5.3 kg
, 1 000

Mangoes bought by Shyama = 3 kg 250 g = d3 + 250 n kg = (3 + 0.25) kg = 3.25 kg
, 1 000
Total fruit bought by Shyama = (5.3 + 3.25) kg = 8.55 kg
800
Oranges bought by Sarla = d4 + nkg = 4.8 kg
, 1 000

45