Answer:
12
Step-by-step explanation:
Short Answer: 18 minutes
Remark
The answer to this problem is less than the smallest time of the two people working together. that fact lets out C and D (38 minutes and 75 minutes). Now you have to choose 15 minutes and 18 minutes. There's a method. No guessing needed.
Givens
Let the time for Sophie = S
Let the time for Simon = M
Let the job to completion = 1
S = 45 minutes
M = 30 minutes
Step One
Convert minutes to hours.
45 minutes = 45 / 60 = 3/4 hour = 0.75 hour
30 minutes = 30 / 60 = 1/2 hour = 0.50 hour
Step Two
Set up the Equation
The formula is a form of job / hour.
Let the time = t that they both have to work
job = 1 in these problems.
1/S + 1/M = 1/t
1/0.75 + 1/0.5 = 1/t
Solve
1 ÷ 0.75 = 1.33333
1 ÷ 0.5 = 2
1.3333 + 2 = 3.33333
3.3333 = 1 / t Multlply both sides by t
3.3333*t = 1
t = 1 / 3.333333333
t = 0.3 of an hour
1 hour = 60 minutes
0.3 hours = x Cross Multiply
x = 60 * 0.3
x = 18 minutes
Answer working together it took them 18 minutes <<<<<
The answer to your question
is 12
<u><em>780 students</em></u>
<u><em></em></u>
<em>Set up a proportion.</em>
<em />
<em>75 / 125 = x/1300</em>
<em />
<em>125 10.4 = 1300</em>
<em />
<em>75 * 10.4 = 780</em>
<em />
<em>x=780</em>
He donated $285 to the salvation army.
The first thing to do is solve for "x". The equation would be {2(3x+60)}+5x+100=550.
Then, you would multiply 2 with 3x and 60. Your new equation would be 5x+120+5x+100=550.
Next, you would combine like terms. This means to combine the terms that are similar. In this case, it would be the whole numbers and the numbers with the variable. Your new equation would be 10x+220=550.
After that, you subtract 220 on both sides of the equal sign. This makes the equation 10x=330.
Then, you divide ten on both sides of the equal sign, giving you x=33.
The second things to is replace the x with 33. The amount for the salvation army is 5x+120. Replacing 33 with x, your final equation will be 165+120=$285.
Have a great day!!! :)
