In a factory, 100 workers are engaged and an average rate of wages is Rs. 5 per hour. Standard working hours per week are 40 hours and the standard output is 10 units per hour. During a week in February, wages were paid for 50 workers @ Rs. 5 per hour, 10 workers @ Rs. 7 per hour and 40 workers @ Rs. 4 per hour. Actual output was 380 units. The factory did not work for 5 hours due to breakdown of machinery. Calculate (i) Labour cost variance; (ii) Labour rate variance; (iii) Labour efficiency variance.