Page 95 - Start Up Mathematics_7

4
2. A star in the Milky Way galaxy is 7 × 10 light years away from the earth and a light year is
12
approximately 5.8 × 10 miles. Find out in scientific form the distance of the star from the
earth in miles.
2
3. Find the area of the following figures (in m ):

4
3
(a) 0.02 × 10 m (b) 0.005 × 10 m

–2
4
0.3 × 10 cm 6,400 × 10 m
4. Heavier elements like iron have greater density (in grams per cubic centimetre) than lighter
elements such as nitrogen. The densities of some of the elements are given in the following
table. Can you arrange them in descending order (from heaviest to lightest)?

Element Density
Oxygen 0.001429

Hydrogen 0.00008388

Helium 0.0001764
Nitrogen 0.0012506

Copper 8.96

Chlorine 0.00295

[Hint: Express each of them in scientific notation.]

Values and Life Skills

The population of a country is about 1,12,000,000. Express it in standard notation.
What are the consequences of high population?

Some NCERT Textbook Questions

1. Identify the greater number, wherever possible, in each of the following?
3
8
3
5
4
(a) 4 or 3 (b) 5 or 3 (c) 2 or 8 2
10
2
(d) 100 or 2 100 (e) 2 or 10 2
2. Express each of the following as product of powers of their prime factors:
(a) 648 (b) 405 (c) 540 (d) 3,600
3. Simplify:
3
2
3
2
(a) 2 × 10 (b) 7 × 2 (c) 2 × 5 (d) 3 × 4 4
2
2
2
2
4
3
(e) 0 × 10 (f) 5 × 3 (g) 2 × 3 (h) 3 × 10 4
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