A mason can build a wall in 70 hours. After 7 hours he takes a break. What fraction of the wall is yet to be built?

A mason makes a wall in 70 hours.

∴ Part of wall built by the mason in 7 hours

$=\frac{7}{70}=\frac{1}{10}$

$\therefore$ Remaining part $=1-\frac{1}{10}$

$=\frac{9}{10}=0.9$