Posted by **Haile** on Thursday, September 29, 2011 at 10:54pm.

Express the repeating decimal 0.513 (the 13 is repeating so the decimal is 0.5131313131313...) as a fraction in lowest terms using the infinite geometric series method.

- Math -
**Reiny**, Thursday, September 29, 2011 at 11:53pm
0.5131313131313...

= .5 + .013131313...

= .5 + .013 + .00013 + .0000013 + ...

= .5 + an infinite geometric series

for the GS, a= .013 , r = .01

sum ∞ = a/(1-r) = .013/(1-.01) = (13/1000) / (99/100)

= 13/990

so sum∞ = 1/2 + 13/990 = 254/495

easier way:

for numerator, write down all digits to the end of the first repeat, from that subtract the digits that don't repeat : 513 - 5 = 508

for denominator, write down a 9 for each repeating digit, followed by a 0 for each non-repeating digit : 990

so ..

.5131313 = 508/990 = 254/495

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