Supplement G - Solution Manual Krajewski Operations Management Processes and Supply 11th Edition - Measuring Output Rates

Supplement


H Measuring Output Rates


PROBLEMS

Time Study Method
1. A machine shop
a. Normal time per cycle = (Average observed time)(Rating factor)
The average observed time is: (40 + 48 + 48 + 46 + 42)/5 = 44.80 min./operation
The normal time per cycle is then:
NTC = t (F )(RF )=(44.80)(1)(0.95)=42.56 min.
b. Standard time = Normal time for the cycle (1.0 + allowance):
ST = NTC (1.0 + A )
= 42.56 (1 + 0.15 )
= 48.94 min.

2 Stetson and Stetson Company
a. Normal time per cycle = (Average observed time)(Rating factor)
The average observed time is: (0.40 + 0.20 + 0.31 + 0.15 + 1.25) = 2.31 minutes
NTC = (2.31)(1.00) = 2.31 min.
ST = (2.31)(1.18) = 2.7258 min.
b. Sample size necessary for 95 percent confidence, i.e., z = 1.96 and error of ± 3
percent:
2
⎡⎛ 1.96 ⎞⎛ 0.021 ⎞ ⎤
For work element 1: n = ⎢⎜ ⎟⎜ ⎟ ⎥ = 11.76
⎣⎝ 0.03 ⎠⎝ 0.400 ⎠ ⎦
2
⎡⎛ 1.96 ⎞⎛ 0.011 ⎞ ⎤
For work element 2: n = ⎢⎜ ⎟⎜ ⎟ ⎥ = 12.91
⎣⎝ 0.03 ⎠⎝ 0.200 ⎠ ⎦
2
⎡⎛ 1.96 ⎞⎛ 0.018 ⎞ ⎤
For work element 3: n = ⎢⎜ ⎟⎜ ⎟ ⎥ = 14.39
⎣⎝ 0.03 ⎠⎝ 0.310 ⎠ ⎦
2
⎡⎛ 1.96 ⎞⎛ 0.005 ⎞ ⎤
For work element 4: n = ⎢⎜ ⎟⎜ ⎟ ⎥ = 4.74
⎣⎝ 0.03 ⎠⎝ 0.150 ⎠ ⎦
2
⎡⎛ 1.96 ⎞⎛ 0.085 ⎞ ⎤
For work element 5: n = ⎢⎜ ⎟⎜ ⎟ ⎥ = 19.73
⎣⎝ 0.03 ⎠⎝ 1.250 ⎠ ⎦


H-1
Copyright © 2016 Pearson Education, Inc.

, H-2 l SUPPLEMENT H Measuring Output Rates l




c. Sample size of 20 is adequate.

3. Bill’s Fast-Food Restaurant

Work
Element 1 2 3 4 5 t RF F NT
1 0.45 0.41 0.50 0.48 0.36 0.44 0.9 1 0.396
2 0.85 0.81 0.77 0.89 0.83 0.83 1.2 1 0.996
3 0.60 0.55 0.59 0.58 0.63 0.59 1.2 1 0.708
4 0.31 0.24 0.27 0.26 0.32 0.28 1.0 1 0.280
Normal time per cycle (NTC), in minutes per burger = 2.380

Standard time = Normal time per cycle (1.0 + allowance)
ST = NTC (1.0 + A)
= 2.380 (1.0 + 0.15 )
= 2.737 min. unit
Employees needed = 300(2.737)/190 = 4.322 or 5 employees (The employees will
have some slack time.)

4. Bill’s Fast-Food Restaurant, continued
a. Work element 3, select time
0.45 + 0.31 + 0.50 + 0.48 + 0.39 + 0.31 + 0.44 + 0.29 + 0.33 + 0.40
t = = 0.390
10
Revised normal time: 0.390 (1) (1.2) = 0.468
b. Revised normal time per cycle.
Work
Element NT
1 0.396
2 0.996
3 0.468
4 0.280
Normal time per cycle, (NTC) = 2.140 min./burger
Revised standard time per cycle
ST = NTC (1.0 + A)
= 2.140 (1.0 + 0.15 )
= 2.461 min. burger
c. Sample size for work element 3,—98 percent confident to be within ± 13 percent
2 2

σ= ∑ (t − t )
i
=
∑ (t − 0.468)
i
= 0.077
n −1 9
2 2
⎡⎛ z ⎞ ⎛ σ ⎞ ⎤ ⎡⎛ 2.33 ⎞⎛ 0.077 ⎞ ⎤
n = ⎢⎜ ⎟⎜ ⎟ ⎥ = ⎢⎜ ⎟⎜ ⎟ ⎥ = 8.7
⎣⎝ p ⎠ ⎝ t ⎠ ⎦ ⎣⎝ 0.13 ⎠⎝ 0.468 ⎠ ⎦
n = 9 , therefore enough observations have been already made.


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