comment calculer ce nombre en ecriture fractionnaire 1+1/7+1/21+1/84+1/140

1 + 1/7 + 1/21 + 1/84 + 1/140
= 1 x 60 / 7 x 60 + 1 x 20 / 21 x 20 + 1 x 3 / 140 x 3
= 60/420 + 21/420 + 3/420
= 81/420 + 3/420
= 84/420
= 84 x 1 / 84 x 5
= 1/5