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Oxana [17]
1 year ago
12

When 7/11 is written as a decimal, what is the sum of the first 20 digits after the decimal point? Pls Help

Mathematics
2 answers:
FromTheMoon [43]1 year ago
8 0

There's a neat trick to finding the rational form of a repeating decimal number. Take for instance x=0.123123123\ldots. Then

x = 0.123123123\ldots \\\\ \implies 1000x = 123.123123\ldots \\\\ \implies 1000x - x = 123.123123\ldots - 0.123123\ldots \\\\ \implies 999x = 123 \\\\ \implies x = \dfrac{123}{999}

It's easy to reverse this method to find the repeating decimal form of \frac7{11}. Let

x = \dfrac7{11}

Multiply the numerator and denominator by 9,

x = \dfrac{63}{99}

It follows that

x = \dfrac{63}{99} \\\\ \implies 99x = 63 \\\\ 100x - x = 63.6363\ldots - 0.6363\ldots \\\\ \implies x = 0.636363\ldots

The first 20 digits after the decimal are made up of 10 each of 3 and 6, so the sum is 10 × (3 + 6) = 90.

Svetlanka [38]1 year ago
5 0

Answer:

90

Step-by-step explanation:

Using long division, we find that  Every group of two digits after the decimal point has a sum of 9 so the sum of the first 20 digits after the decimal point is 10*9=90

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