Ratio of wages = (3 x 20) : (2 x 30) : (1 x 36)
= 5: 5: 3
Total wages of 20 men = 5/13 =Rs.300
∴ Wages of a man = Rs.15.
Similarly, wages of 30 women (5/30) x 780 = Rs.300
Wages of a woman = Rs.10
and wages of 36 children (3/13) x 780 = Rs.180
Wages of a child = Rs.5
∴ Total wages of 15 men, 21 women and 30 children
= 15 x 15 + 21 x 10 + 30 x 5
= Rs.585
∴ Total wages for 2 weeks = Rs.1170.