Simple...

Suppose he sells  100cm (1m) cloth for Rs. 140(40% profit). But his actual profit is only 39%

That means on an average he is getting only  Rs 139(39% profit) for every 100 cm he sells though he charges Rs.140 for 100cm. That means the tape he uses is longer. To find out the extended length of the tape:

100*140= x * 139 where x is the length of the tape he uses

Length of the tape = 100.719

Increased length = .719

Rgrds,

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