Hundred Fractions is More Than Enough

Algebra Level 4

2 1 + 2 3 + 4 3 + 4 5 + 6 5 + 6 7 + + 100 th term \frac{2}{1} + \frac{2}{3} + \frac{4}{3} + \frac{4}{5} + \frac{6}{5} + \frac{6}{7} + \ldots + \text{ 100}^{\text{th}} \text{ term}

If the expression above is simplified to the closed form of m n \frac m n where m , n m,n are coprime positive integers. What is the value of m + n m+n ?

Note - this problem is a part of the sets - 3's & 4's & QuEsTiOnS .


The answer is 10301.

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2 solutions

Brock Brown
Mar 25, 2015

Python 2.7:

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from fractions import Fraction as frac
def odds_gen():
    yield 1
    n = 3
    while True:
        yield n
        yield n
        n += 2
def evens_gen():
    n = 2
    while True:
        yield n
        yield n
        n += 2
odds = odds_gen()
evens = evens_gen()
total = 0
for i in xrange(100):
    total += frac(next(evens),next(odds))
print total.numerator+total.denominator

Mas Mus
Apr 28, 2015

2 1 + ( 2 3 + 4 3 ) + ( 4 5 + 6 5 ) + ( 6 7 + 8 7 ) + + ( 98 99 + 100 99 ) + 100 101 = 2 + 49 × 2 + 100 101 = 100 + 100 101 = 10200 101 \frac{2}{1}+\left(\frac{2}{3}+\frac{4}{3}\right) +\left(\frac{4}{5}+\frac{6}{5}\right)+\left(\frac{6}{7}+\frac{8}{7}\right)+\ldots+\left(\frac{98}{99}+\frac{100}{99}\right)+\frac{100}{101}\\=2+49\times{2}+\frac{100}{101}=100+\frac{100}{101}=~\frac{10200}{101} .

Thus, the required answer is 10200 + 101 = 10301 ~~10200+101=\boxed{10301}

Moderator note:

Nice way to combining "like" terms. Good job!

I used the same method!

Lee Isaac - 5 years, 8 months ago

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