please? Convert the decimal expansion 0.1777... into a rational number. (simplify
Accepted Solution
A:
The three dots after the 777 indicate that the pattern repeats forever. Specifically the 7s go on forever (the 1 does not repeat and its only listed one time)
Let x = 0.1777... The goal is to find the value of x in terms of a fraction of whole numbers (eg like 2/3 or 4/5)
The trick is to somehow get the decimal portion that goes on forever to go away. We will do this through subtraction. But first, we need to do a bit of side work.
Multiply both sides of the equation above by 10 x = 0.1777... 10*x = 10*0.1777... 10x = 1.777... Notice how this moves the decimal over 1 spot to the right
Then go back to the original equation for x and multiply both sides by 100 x = 0.1777... 100*x = 100*0.1777... 100x = 17.777... Now the decimal is moved over two spots to the right
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In summary so far, we have 10x = 1.777... 100x = 17.777...
If we subtract 100x - 10x then we'll have
100x - 10x = (17.777...) - (1.777...) 90x = 16
The decimal portion 777... cancels out when we subtract. This is because the terms line up perfectly and subtract to 0
The last few steps is to solve 90x = 16 for x. We divide both sides by 90 and then reduce as much as possible
90x = 16 90x/90 = 16/90 x = 16/90 x = 8/45
Therefore the final answer is the fraction 8/45
I recommend you use a calculator to confirm that 8/45 will have the decimal form of 0.1777...
Note: your calculator may round the last digit from 7 to an 8