The ages of the 6 members of a colony welfare committee add up to 246 years today. Two of them, now aged 58 and 62, will step down exactly 3 years from now. What will the ages of the remaining 4 members add up to at that time?

The four who stay total 246 - 58 - 62 = 126 years today. In 3 years each of those four has gained 3 years, so their total becomes $126+4\times 3=138$ years. 126 forgets that the four go on ageing. 144 adds $6\times 3=18$ years, ageing all six even though two have left. 264 is the whole committee's total in 3 years (246 + 18), with the two departures never taken out.