IE 131 Homework Problems due Mar 19, 2008 (Chs 13, 14, 15, and 16)
13.5 The continuous timing method is used to direct time study a manual task cycle consisting of
four elements: a, b, c, and d. Two parts are produced each cycle. Element d is an irregular element
performed once every six cycles. All elements were performance rated at 90%. The PFD allowance
is 11%. Determine (a) the normalized time for the cycle and (b) the standard time per part. (c) If
the worker completes 844 parts in an 8hour shift during which she works 7 hours and 10 min,
what is the worker’s efficiency?
Element
a
b
c
d
Observed time (min)
0.35
0.60
0.86
1.46
Solution
: (a)
T
n
= (0.86 + 0.60/6)(0.90) = 0.864 min per cycle
(b) With two parts per cycle, the standard time per part is:
T
std
= 0.864(1 + 0.11)/2 = 0.4795 = 0.48 min
(c)
H
std
= 844(0.48)/60 = 6.752 hr
E
w
= 6.752/8.0 = 0.844 = 84.4%
13.7 The time and performance rating values in the table below were obtained using the
snapback timing method on the work elements in a certain manual repetitive task. All elements
are workercontrolled. All elements were performance rated at 85%. Element e is an irregular
element performed every five cycles. A 15% PFD allowance is applied to the cycle. Determine (a)
the normal time and (b) the standard time for this cycle. If the worker’s performance during actual
production is 125% on all manual elements for seven actual hours worked on an eighthour shift,
(c) how many units will be produced and (d) what is the worker’s efficiency?
Work element
a
b
c
d
e
Observed time (min)
0.61
0.42
0.76
0.55
1.10
Solution
: (a)
T
n
= (0.61 + 0.42 + 0.76 + 0.55 + 1.10/5)(0.85) = 2.176 min
(b)
T
std
= 2.176(1 + 0.15) = 2.502 min
(c) Worker performance
P
w
= 125% for 7.0 hr actually worked in an 8hour shift
T
c
=
T
n
/
P
w
= 2.176/1.25 = 1.741 min
Q
= 7(60)/1.741 = 241.2 rounded down to 241 pc
(d)
H
std
= 241(2.502)/60 = 10.05 hr, and
E
w
= 10.05/8.0 = 1.256 = 125.6%
13.9 The continuous timing method in direct time study was used to obtain the element times for a
workermachine task as indicated in the table below. Element c is a machinecontrolled element
and the time is constant. Elements a, b, d, e, and f are operatorcontrolled and external to the ma
chine cycle, and were performance rated at 80%. If the machine allowance is 25%, and the worker
allowance for personal time, fatigue, and delays is 15%, determine (a) the normal time and (b)
standard time for the cycle. (c) If the worker completed 360 work units working 7.2 hours on an 8
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 Spring '08
 Groover
 Normal Distribution, Tn, Normal time

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