Page 52 - Start Up Mathematics_7

Money
To buy or sell anything, we need money. It comes in the form of currency notes or coins. The
Indian currency is rupees (`).
We know that 100 paise makes 1 rupee. To convert rupee into paise, we multiply the number of
rupees by 100 and to convert paise into rupees we divide the number of paise by 100.

i.e., 100 paise = ` 1
1
⇒ 1 paisa = ` ⇒ 1 paisa = ` 0.01
100
Length

In the metric system of measurement, the standard unit of length is metre (m). In daily life, we
also use another unit of length, i.e., kilometre for measuring large distances.

We know that 100 centimetres make 1 metre. To convert metres into centimetres, we multiply
metres by 100 and to convert centimetres into metres, we divide centimetres by 100.
i.e., 100 cm = 1 m
1
⇒ 1 cm = m ⇒ 1 cm = 0.01 m
100
Mass

When you weigh something, you actually find its mass. In the metric system of measurement, the
standard unit of mass is kilogram (kg). It is the most commonly used unit which we use in our
daily life.
We know that 1,000 grams make 1 kilogram. To convert kilograms into grams, we multiply
kilograms by 1,000 and to convert grams into kilograms, we divide grams by 1,000.

i.e., 1,000 g = 1 kg
1
⇒ 1 g = kg ⇒ 1 g = 0.001 kg
1,000

• While dealing with problems involving money, length or mass, we must ensure that all the units are
same. In other words, if in a problem different units are given we first convert them into the same units
and then proceed.
• For example, if in a question, m, km and dm are used to represent length, we should first convert all of
them into same unit and then start solving the question.
Example 4: Express as rupees using decimals:

(a) 18 paise (b) 325 paise (c) 88 rupees 88 paise
18
Solution: (a) 18 paise = ` = ` 0.18
100
325
(b) 325 paise = = ` 3.25
100
(c) 88 rupees 88 paise = 88 + 88 rupees = ` 88.88
100
Example 5: (a) Express 7 cm in m and km.

(b) Express 45 mm in cm, m and km.

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