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Express the following recurring decimal as a rational number: 3.5. - Mathematics and Statistics

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Question

Express the following recurring decimal as a rational number:

`3.dot5`

Sum

Solution

`3.dot5`

= 3.555…

= 3 + 0.5 + 0.05 + 0.005 + …

Here, 0.5, 0.05, 0.005, … are in G.P. with a = 0.5 and r = 0.1.

Since |r| = |0.1| < 1

∴ Sum to infinity exists.

∴ Sum to infinity = `"a"/(1 - "r")`

= `0.5/(1 - (0.1))`

= `0.5/0.9`

= `5/9`

∴ `3.dot5 = 3 + 5/9 = 32/9`

shaalaa.com
Recurring Decimals
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Chapter 4: Sequences and Series - EXERCISE 4.3 [Page 57]

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