The correct answer is: C. a-3, b-1, c-4, d-2
- Overhead efficiency variance is the difference between the actual overhead cost and the budgeted overhead cost, adjusted for the actual volume of production. It is caused by inefficient use of resources, such as using more labor hours than necessary to produce a product.
- Overhead volume variance is the difference between the actual overhead cost and the budgeted overhead cost, adjusted for the actual volume of production. It is caused by a difference between the actual volume of production and the budgeted volume of production.
- Labour idle time variance is the difference between the actual labour hours used and the standard labour hours allowed, multiplied by the standard wage rate. It is caused by workers being idle for reasons such as machine breakdowns or waiting for materials.
- Labour efficiency variance is the difference between the actual labour hours used and the standard labour hours allowed, multiplied by the standard wage rate. It is caused by workers working less efficiently than expected, such as taking longer breaks or making more mistakes.
In the question, option A is incorrect because labour idle time variance is caused by workers being idle for reasons such as machine breakdowns or waiting for materials, not by appointing low grade employees. Option B is incorrect because overhead volume variance is caused by a difference between the actual volume of production and the budgeted volume of production, not by power failure. Option D is incorrect because labour efficiency variance is caused by workers working less efficiently than expected, not by poor working conditions.