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3 years ago

a teacher had 21 red pens. if the ratio of red pens to blue pens she owned was 3:1 , how many pens did she have in total

Mathematics

2 answers:

snow_lady [41]3 years ago

8 0

She had 21:7 because if you multiply 3:1 by 7 each it is 21:7 so she had 7 blue pens

erma4kov [3.2K]3 years ago

5 0

There are 21 red pens. For every 3 red pens, there is 1 blue pen.
Let's make these into a fraction equation.
21/p=3/1
p is the number of blue pens we have yet to find.
First, cross multiply.
21x1=21
px3=3p
Now, we have an equation of
21÷3p
We set it equal to 1, and we solve it.
21÷3p = 1
(21÷3p)×3p=1×3p
21=3p
21÷3=(3p)÷3
7=p
So, if there are 21 red pens, there are 7 blue pens.
We add these together to find the total number of pens the teacher has.
21+7=28
The teacher has 28 pens total.

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Dafna1 [17]

The better deal is 1 gallon of milk for $3.

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3 years ago

A radioactive substance decays exponentially. A scientist begins with 190 milligrams of a radioactive substance. After 19 hours,

Lelu [443]

Answer:

51 milligrams

Step-by-step explanation:

Exponential growth or decay can be modeled by the equation ...

y = a·b^(x/c)

where 'a' is the initial value, 'b' is the "growth factor", and 'c' is the time period over which that growth factor applies. The time period units for 'c' and x need to be the same.

In this problem, we're told the initial value is a = 190 mg, and the value decays to 95 mg in 19 hours. This tells us the "growth factor" is ...

b = 95/190 = 1/2

c = 19 hours

Then, for x in hours the remaining amount can be modeled by ...

y = 190·(1/2)^(x/19)

After 36 hours, we have x=36, so the remaining amount is ...

y = 190·(1/2)^(36/19) ≈ 51.095 . . . . milligrams

About 51 mg will remain after 36 hours.

8 0

2 years ago

A bag contains 240 marbles that are either red, blue, or green. The ratio of red to blue to green marbles is 5:2:1. If one-third

Andrej [43]

The fraction of the remaining marbles in the bag will be blue is 6/17.

<h3>What fraction of the remaining marbles in the bag will be blue?</h3>

The first step is to determine the initial number of marbles in the bag:

Initial number of red marbles in the bag : (5/8) x 240 = 150

Initial number of blue marbles in the bag : (2/8) x 240 = 60

Initial number of green marbles in the bag : 240 - 150 - 60 = 30

Number of red marbles remaining after 1/3 is removed = (1 - 1/3) x 150

2/3 x 150 = 100

Number of green marbles remaining after 2/3 is removed = (1 - 2/3) x 30

1/3 x 30 = 10

Total number of marbles now in the bag : 100 + 10 + 60 = 170

Fraction of blue marbles = 60 / 170 = 6/17

To learn more about ratios, please check: brainly.com/question/9194979

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7 0

2 years ago

Please answer this in two minutes

diamong [38]

Answer:

366.6 mm²

Step-by-step explanation:

Step 1: find XY using the Law of sines.

Thus,

$\frac{XY}{sin(W)} = \frac{WY}{sin(X)}$

m < W = 180 - (70+43) (sum of angles in a triangle)

W = 180 - 113 = 67°

WY = 24 mm

X = 43°

XY = ?

$\frac{XY}{sin(67)} = \frac{24}{sin(43)}$

Cross multiply:

$XY*sin(43) = 24*sin(67)$

$XY*0.68 = 24*0.92$

Divide both sides by 0.68 to solve for XY

$\frac{XY*0.68}{0.68} = \frac{24*0.92}{0.68}$

$XY = 32.47$

XY ≈ 32.5 mm

Step 2: find the area using the formula, ½*XY*WY*sin(Y).

Area = ½*32.5*24*sin(70)

Area = ½*32.5*24*0.94

= 32.5*12*0.94

Area = 366.6 mm² (nearest tenth)

6 0

3 years ago

The number of people estimated to vote in an election was 7000. The actual number of people who voted was 5600

baherus [9]

Answer:

If you mean the percentage error then look at this

Step-by-step explanation:

% error = Estimated - Actual x 100

Estimated. 1

% error = 7000 - 5600 x 100

7000. 1

% error = 1400 x 100

7000

% error = 140000/7000

% error = 20%

6 0

2 years ago