Hi all.. case I: Drop 123 vs 456 in pendulum if both has same weight then put all six balls aside and its easy to find lightest ball in another two balls(7 & 8) with in two weighings. Case II: Drop 123 vs 456 in pendulum if any side has more weight than automatically we can find lightest ball among those three by weighting it in pendulum by second time... Its quite easy..:-)
1st Weight = 123 balls Vs 456balls; if matched then2nd Weight = 7 Vs 8