[tex] \frac{1}{2}+ \frac{1}{6}+ \frac{1}{12}+ \frac{1}{20}+ \frac{1}{30}+ \frac{1}{42}+ \frac{1}{56}+ \frac{1}{72}+ \frac{1}{90} [/tex]
2 = 2
6 = 2 * 3
12 = 2² * 3
20 = 2² * 5
30 = 2 * 3 * 5
42 = 2 * 3 * 7
56 = 2³ * 7
72 = 2³ * 3²
90 = 2 * 3² * 5
cmmmc = 2³ * 3² * 5 * 7 = 2520
[tex] \frac{1260+420+210+126+84+60+45+35+28}{2520}= \frac{2268}{2520}= \frac{9}{10} [/tex]
