Chapter 10, Problem 25P

a)

Summary Introduction

To determine: The normal time for the operation

Introduction: Time study is the basis that helps set the standard time; it would time a sample of the performance of the worker.

Answer to Problem 25P

Thenormal time calculated as 3.23 minutes.

Explanation of Solution

Given information:

The allowance for tasks is given as 7% for personal, 10% for fatigue, and 3% for delay. The observed time and performance rating for each element is given as follows:

Element	Performance rating	Observation (minutes per cycle)
		1	2	3	4	5
1	110%	0.5	0.4	0.6	0.4	0.4
2	95%	0.6	0.8	0.7	0.6	0.7
3	90%	0.6	0.4	0.7	0.5	0.5
4	85%	1.5	1.8	2	1.7	1.5

Formulae to calculate normal time:

$\text{Average time}=\frac{\text{Observations}}{n}$

$\text{Normal time}=\text{Average time}\times \text{Performance rating}$

Calculate the normal time:

Element	Performance rating	Observation (minutes)					Average time	Normal time
		1	2	3	4	5
1	110%	0.5	0.4	0.6	0.4	0.4	0.46	0.51
2	95%	0.6	0.8	0.7	0.6	0.7	0.68	0.65
3	90%	0.6	0.4	0.7	0.5	0.5	0.54	0.49
4	85%	1.5	1.8	2	1.7	1.5	1.7	1.45

Excel worksheet:

Calculate the average time for the first element:

$\begin{array}{c}\text{Average time}=\frac{\text{Observation}}{n}\\ =\frac{0.5+0.4+0.6+0.4+0.4}{5}\\ =\frac{2.3}{5}\\ =0.46\text{ minutes}\end{array}$

The average time is calculated by taking an average of the observation given, which is summation of 0.5, 0.4, 0.6, 0.4, and 0.4 and dividing the result by 5. Hence, the average is 0.46 minutes.

Calculate the average time for the second element:

$\begin{array}{c}\text{Average time}=\frac{\text{Observation}}{n}\\ =\frac{0.6+0.8+0.7+0.6+0.7}{5}\\ =\frac{3.4}{5}\\ =0.68\text{ minutes}\end{array}$

The average time is calculated by taking an average of the observation given, which is summation of 0.6, 0.8, 0.7, 0.6, and 0.7 and dividing the result by 5. Hence, the average is 0.68 minutes.

Calculate the average time for the third element:

The average time is calculated by taking an average of the observation given, which is summation of 0.6, 0.4, 0.7 0.5, and 0.5 and dividing the result by 5. Hence, the average is 0.54 minutes.

$\begin{array}{c}\text{Average time}=\frac{\text{Observation}}{n}\\ =\frac{0.6+0.4+0.7+0.5+0.5}{5}\\ =\frac{2.7}{5}\\ =0.54\text{ minutes}\end{array}$

Calculate the average time for the fourth element:

The average time is calculated by taking an average of the observation given, which is summation of 1.5, 1.8, 2.0, 1.7, and 1.5 and dividing the result by 5. Hence, the average is 1.7 minutes.

$\begin{array}{c}\text{Average time}=\frac{\text{Observation}}{n}\\ =\frac{1.5+1.8+2.0+1.7+1.5}{5}\\ =\frac{8.5}{5}\\ =1.7\text{ minutes}\end{array}$

Calculate the normal time for the first element:

The normal time is calculated by multiplying the average time and performance rating. The average time is calculated as 0.46 minutes, and performance rating is given as 110%. Hence, the normal time is 0.51 minutes.

$\begin{array}{c}\text{Normal time}=\text{Average time}\times \text{Performance rating}\\ =0.46\times 110\%\\ =0.46\times 1.1\\ =0.51\text{ minutes}\end{array}$

Calculate the normal time for the second element:

The normal time is calculated by multiplying the average time and performance rating. The average time is calculated as 0.68 minutes, and performance rating is given as 95%. Hence, the normal time is 0.65 minutes.

$\begin{array}{c}\text{Normal time}=\text{Average time}\times \text{Performance rating}\\ =0.68\times 95\%\\ =0.68\times 1.05\\ =0.65\text{ minutes}\end{array}$

Calculate the normal time for the third element:

The normal time is calculated by multiplying the average time and performance rating. The average time is calculated as 0.54 minutes, and performance rating is given as 90%. Hence, the normal time is 0.49 minutes.

$\begin{array}{c}\text{Normal time}=\text{Average time}\times \text{Performance rating}\\ =0.54\times 90\%\\ =0.54\times 0.90\\ =0.49\text{ minutes}\end{array}$

Calculate the normal time for the fourth element:

The normal time is calculated by multiplying the average time and performance rating. The average time is calculated as 1.7 minutes, and performance rating is given as 85%. Hence, the normal time is 1.45 minutes.

$\begin{array}{c}\text{Normal time}=\text{Average time}\times \text{Performance rating}\\ =1.7\times 85\%\\ =1.7\times 0.85\\ =1.45\text{ minutes}\end{array}$

Calculate the total normal time:

The normal time is calculated by adding the normal time of all the elements.

$\begin{array}{c}\text{Normal time}=\text{Sum of normal times}\\ =0.51+0.65+0.49+1.45\\ =3.08\text{ minutes}\end{array}$

Hence, the total normal time is 3.08 minutes.

b)

Summary Introduction

To determine: The standard time for the operation.

Introduction: Time study is the basis that helps set the standard time, it would time a sample of the performance of the worker.

Answer to Problem 25P

Thestandard time is calculated as 5.4 minutes.

Explanation of Solution

Given information:

The allowance for tasks is given as 7% for personal, 10% for fatigue, and 3% for delay. The observed time and performance rating for each element are given as follows:

Element	Performance rating	Observation (minutes per cycle)
		1	2	3	4	5
1	110%	0.5	0.4	0.6	0.4	0.4
2	95%	0.6	0.8	0.7	0.6	0.7
3	90%	0.6	0.4	0.7	0.5	0.5
4	85%	1.5	1.8	2	1.7	1.5

Formulae to calculate standard time:

$\text{Allowance factor}=\text{Personal}+\text{Fatigue}+\text{Delay}$

$\text{Standard time}=\frac{\text{Normal time}}{1-\text{Allowance factor}}$

Calculate the allowance factor:

The allowance factor is calculated by adding personal allowance, fatigue, and delay allowance. Personal allowance is given as 7%, fatigue is 10%, and delay allowance is 3%. Hence, the allowance factor is 20%.

$\begin{array}{c}\text{Allowance factor}=\text{Personal}+\text{Fatigue}+\text{Delay}\\ =7\%+10\%+3\%\\ =20\%\end{array}$

Calculate the standard time:

The standard time is calculated by dividing the normal time with the value attained by subtracting the allowance factor from 1. The normal time is calculated as 3.08 minutes and the allowance factor is calculated as 20%

$\begin{array}{c}\text{Standard time}=\frac{\text{Normal time}}{1-\text{Allowance factor}}\\ =\frac{3.08\text{ minutes}}{1-0.20}\\ =\frac{\text{3}\text{.08 minutes}}{0.80}\\ =3.85\text{ minutes}\end{array}$

Hence, the standard time is 3.85 minutes.