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A Peek Beyond the Point - More on the Decimal System

Grade 7CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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The decimal system extends the place value system to represent parts of a whole using a decimal point. The places to the right of the decimal point are Tenths (110\frac{1}{10}), Hundredths (1100\frac{1}{100}), and Thousandths (11000\frac{1}{1000}).

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To compare two decimal numbers, first compare the whole number parts. If they are equal, compare the tenths digit. If those are also equal, compare the hundredths digit, and so on.

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Decimals are used to convert units: 1 paisa=₹1100=₹0.011 \text{ paisa} = ₹ \frac{1}{100} = ₹ 0.01, 1 g=11000 kg=0.001 kg1 \text{ g} = \frac{1}{1000} \text{ kg} = 0.001 \text{ kg}, and 1 cm=1100 m=0.01 m1 \text{ cm} = \frac{1}{100} \text{ m} = 0.01 \text{ m}.

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When multiplying a decimal by 10,100, or 100010, 100, \text{ or } 1000, the decimal point shifts to the right by as many places as there are zeros.

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When dividing a decimal by 10,100, or 100010, 100, \text{ or } 1000, the decimal point shifts to the left by as many places as there are zeros.

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To multiply two decimals, multiply them as if they were whole numbers. The number of decimal places in the product is the sum of the decimal places in the two factors.

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To divide a decimal by another decimal, multiply both the dividend and the divisor by a power of 1010 (like 10,100,100010, 100, 1000) to make the divisor a whole number, then divide.

📐Formulae

Total decimal places in product=Places in factor 1+Places in factor 2\text{Total decimal places in product} = \text{Places in factor 1} + \text{Places in factor 2}

1.0=1010=11.0 = \frac{10}{10} = 1

Value×10n→Shift decimal n places to the right\text{Value} \times 10^n \rightarrow \text{Shift decimal } n \text{ places to the right}

Value÷10n→Shift decimal n places to the left\text{Value} \div 10^n \rightarrow \text{Shift decimal } n \text{ places to the left}

💡Examples

Problem 1:

Add 25.6725.67 and 14.3814.38.

Solution:

25.67+14.3840.05\begin{array}{r} 25.67 \\ + 14.38 \\ \hline 40.05 \end{array}

Explanation:

Align the decimal points vertically and add column by column, carrying over just like whole number addition.

Problem 2:

Multiply 2.52.5 by 0.130.13.

Solution:

2.5×0.13=0.3252.5 \times 0.13 = 0.325

Explanation:

First, multiply 2525 and 1313 as whole numbers: 25×13=32525 \times 13 = 325. The number of decimal places in 2.52.5 is 11 and in 0.130.13 is 22. Total decimal places needed is 1+2=31 + 2 = 3. Placing the point gives 0.3250.325.

Problem 3:

Divide 30.9430.94 by 0.70.7.

Solution:

30.94÷0.7=30.940.7=309.47=44.230.94 \div 0.7 = \frac{30.94}{0.7} = \frac{309.4}{7} = 44.2

Explanation:

To make the divisor 0.70.7 a whole number, multiply both numerator and denominator by 1010. This converts the problem to 309.4÷7309.4 \div 7, which equals 44.244.2.