Question

1 supra 10 ori 11 plus 1 supra 11 ori 12 plus 1 supra 12 ori 13 plus 1 supra 13 ori 14 plus 1 supra 14 ori 15

Answer 1

folosesti formula 1/n-1/n+1=1/n*(n+1)
si obtii:
1/10*11+1/11*12+1/12*13+1/13*14+1/14*15=1/10-1/11+1/11-1/12+1/12-1/13+1/13-1/14+1/14-1/15=1/10-1/15=3/30-2/30=1/30