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Math Problems
Grade 8
Percent of change: word problems
In a newspaper, it was reported that the number of yearly robberies in Springfield in
2012
2012
2012
was
235
235
235
, and then went down by
40
%
40 \%
40%
in
2013
2013
2013
. How many robberies were there in Springfield in
2013
2013
2013
?
\newline
Answer:
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In a newspaper, it was reported that the number of yearly robberies in Springfield in
2010
2010
2010
was
200
200
200
, and then went down by
4
%
4 \%
4%
in
2011
2011
2011
. How many robberies were there in Springfield in
2011
2011
2011
?
\newline
Answer:
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In a newspaper, it was reported that the number of yearly robberies in Springfield in
2010
2010
2010
was
150
150
150
, and then went down by
50
%
50 \%
50%
in
2011
2011
2011
. How many robberies were there in Springfield in
2011
2011
2011
?
\newline
Answer:
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in the west region of the US, the ratio of densely vegetated land to sparsely vegetated land is
11
:
18
11:18
11
:
18
, in the central region of the US, the ratio is
3
:
13
3:13
3
:
13
. What is the difference in percentage of densely vegetated land from the west region to the central region?
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In
2000
2000
2000
, there were
0.025
0.025
0.025
phone subscriptions per person in Africa for both mobile and land-line phones. After that, the land-line phone subscriptions steadily increased by
0.01
0.01
0.01
every
7
7
7
years, while the mobile phone subscriptions grew
48
%
48\%
48%
per year. What was the total number of phone subscriptions per person in
2002
2002
2002
?
\newline
Choose
1
1
1
answer:
\newline
(A)
0.027
0.027
0.027
\newline
(B)
0.034
0.034
0.034
\newline
(C)
0.073
0.073
0.073
\newline
(D)
0.083
0.083
0.083
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During one time period, the price of rhodium increased at a rate that was proportional to the price of rhodium at that time.
\newline
The price for an ounce of rhodium was
$
475
\$ 475
$475
initially, and it quadrupled every
25
25
25
months.
\newline
What was the price for an ounce of rhodium after
18
18
18
months?
\newline
Choose
1
1
1
answer:
\newline
(A)
$
175
\$ 175
$175
\newline
(B)
$
1048
\$ 1048
$1048
\newline
(C)
$
1289
\$ 1289
$1289
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In March, Delphine's house had
40
%
40 \%
40%
more snowfall than in February. Delphine's house had
f
f
f
centimeters of snowfall in February.
\newline
Which of the following expressions could represent how much snowfall Delphine had at her house in March?
\newline
Choose
2
2
2
answers:
\newline
(A)
40
f
40 f
40
f
\newline
(B)
40
+
f
40+f
40
+
f
\newline
(C)
1.4
f
1.4 f
1.4
f
\newline
(D)
40
f
+
f
40 f+f
40
f
+
f
\newline
(E)
4
10
f
+
f
\frac{4}{10} f+f
10
4
f
+
f
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Ayden had a goal of finishing painting at least
80
%
80 \%
80%
of the
500
500
500
square meters of a house's walls by today. He actually finished painting
415
415
415
square meters today.
\newline
Did Ayden meet his goal? Why?
\newline
yes / no Ayden painted
□
\square
□
square meters more / less than his goal.
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A gumball machine contains
23
23
23
green gumballs,
52
52
52
red gumballs,
34
34
34
blue gumballs,
61
61
61
yellow gumballs, and
30
30
30
pink gumballs.
\newline
What percentage of the gumballs are red?
\newline
%
\%
%
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In our solar system,
6
6
6
of the
8
8
8
planets have moons.
\newline
What percentage of the planets have moons?
\newline
%
\%
%
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Of all the species in the world,
4
4
4
out of every
5
5
5
are insects.
\newline
What percentage of species are insects?
\newline
%
\%
%
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In the United States,
13
13
13
out of every
20
20
20
cans are recycled.
\newline
What percent of cans are recycled?
\newline
%
\%
%
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An estimated
3
3
3
out of every
25
25
25
men are left-handed.
\newline
What percent of men are lefthanded?
\newline
%
\%
%
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There are
25
25
25
students in Ms. Nguyen's second-grade class. In the class election,
4
4
4
students voted for Benjamin,
12
12
12
voted for Sahil, and
9
9
9
voted for Maria.
\newline
What percentage of the class voted for Maria?
\newline
%
\%
%
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A coin contains
9
9
9
grams of nickel and
16
16
16
grams of copper, for a total weight of
25
25
25
grams.
\newline
What percentage of the metal in the coin is copper?
\newline
%
\%
%
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Kong took
15
%
15 \%
15%
fewer seconds than Nolan took to complete his multiplication timed test. Kong took
85
85
85
seconds.
\newline
How many seconds did Nolan take? seconds
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A spider ate
25
%
25 \%
25%
more bugs this month than last month. The spider ate
8
8
8
bugs last month.
\newline
How many bugs did the spider eat this month?
\newline
bugs
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A swimming pool had
2
2
2
.
5
5
5
million liters of water in it. Some water evaporated, and then the pool only had
2
2
2
million liters of water in it.
\newline
What percent of the water evaporated?
\newline
%
\%
%
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A brand of cereal had
1
1
1
.
2
2
2
milligrams
(
m
g
)
(\mathrm{mg})
(
mg
)
of iron per serving. Then they changed their recipe so they had
1.8
m
g
1.8 \mathrm{mg}
1.8
mg
of iron per serving.
\newline
What was the percent increase in iron?
\newline
%
\%
%
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Savanna had
40
40
40
iris blooms last year. This year, she had
15
%
15 \%
15%
more iris blooms.
\newline
How many more iris blooms did Savanna have this year?
\newline
blooms
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Oliver read for
450
450
450
minutes this month. His goal is to read for
10
%
10 \%
10%
more minutes next month.
\newline
If Oliver meets his goal, how many minutes will he read in all during the two months?
\newline
minutes
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There are
20
%
20 \%
20%
more goblins than wizards in magic club. There are
120
120
120
goblins in magic club.
\newline
How many wizards are in the magic club?
\newline
wizards
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In a video game, Val scored
30
%
30 \%
30%
fewer points than Peeta. Peeta scored
1060
1060
1060
points.
\newline
How many points did Val score? points
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Tapiwa raked
5
%
5 \%
5%
more leaves than Adam raked. Tapiwa raked
357
357
357
liters of leaves.
\newline
How many liters of leaves did Adam rake?
\newline
liters
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Finley's pumpkin had a mass of
6
6
6
.
5
5
5
kilograms
(
k
g
)
(\mathrm{kg})
(
kg
)
before he carved it. After it was carved, the pumpkin had a mass of
3.9
k
g
3.9 \mathrm{~kg}
3.9
kg
.
\newline
What was the percent decrease in the mass of the pumpkin?
\newline
%
\%
%
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The family size bottle of sunscreen holds
12
12
12
fluid ounces (
f
l
o
z
\mathrm{fl} \mathrm{oz}
fl
oz
) of sunscreen. The regular bottle holds
75
%
75 \%
75%
less.
\newline
How many fewer fluid ounces does the regular bottle of sunscreen hold?
\newline
fl oz
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Mafalda has a save percentage of
0
0
0
.
738
738
738
so far this hockey season. Last season, her save percentage was
0
0
0
.
585
585
585
.
\newline
How much has Mafalda's save percentage improved?
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A new shopping mall records
120
120
120
total shoppers on their first day of business. Each day after that, the number of shoppers is
10
%
10 \%
10%
more than the number of shoppers the day before.
\newline
What is the total number of shoppers that visited the mall in the first
7
7
7
days?
\newline
Round your final answer to the nearest integer.
\newline
shoppers
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Percent transmittance is the percent of light that passes through an object. If
780
780
780
watts per square meter
(
W
m
2
)
\left(\frac{\mathrm{W}}{\mathrm{m}^{2}}\right)
(
m
2
W
)
of light strike the roof of a greenhouse, and the roof has an
85
%
85 \%
85%
transmittance, how many
W
m
2
\frac{\mathrm{W}}{\mathrm{m}^{2}}
m
2
W
of light pass through the roof?
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An empty pool has the capacity to hold
2700
2700
2700
cubic feet
(
f
t
3
)
\left(\mathrm{ft}^{3}\right)
(
ft
3
)
of water. A particular hose fills this pool with water at a rate of
25
f
t
3
25 \mathrm{ft}^{3}
25
ft
3
per minute. If the hose is placed into the empty pool and turned on, approximately what percent of the pool will be filled with water after
1
1
1
hour?
\newline
Choose
1
1
1
answer:
\newline
(A)
10
%
\mathbf{1 0 \%}
10%
\newline
(B)
44
%
44 \%
44%
\newline
(C)
56
%
56 \%
56%
\newline
(D)
93
%
93 \%
93%
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A chef has a large container full of olive oil. In one night, after he used
25
25
25
quarts of olive oil,
35.9
%
35.9 \%
35.9%
of the full container of olive oil remained. To the nearest whole quart, how many quarts of olive oil remained in the container?
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In a random sample of Amir's customer feedback,
96
%
96 \%
96%
of customers gave Amir positive feedback. At this rate, how many of Amir's
900
900
900
customers gave him positive feedback?
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A small pendulum is released in water. The maximum height that the pendulum reaches each time it swings decreases over time. Every
180
180
180
seconds, the pendulum's maximum height is reduced by
90
%
90 \%
90%
. If the pendulum has been swinging for
360
360
360
seconds and now reaches a maximum height of
0
0
0
.
031
031
031
centimeters, what was the maximum height of the pendulum, in centimeters, when it was initially released?
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On Monday, Harry had
75
%
75 \%
75%
as many toys as Teddy did. On Tuesday, Harry acquires
32
32
32
more toys, and Teddy acquires
15
%
15 \%
15%
as many toys as he had on Monday. If Harry and Teddy now have the same number of toys, how many toys did Harry have on Monday?
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Zaid and Matias, two farmers, constructed a
792
792
792
-foot fence around their very large garden. If Zaid constructed
20
%
20 \%
20%
more of the fence than Matias did, how many feet of the fence did Zaid construct?
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