In this problem, the sum of the cats and dogs must equal 15. If there are 10 dogs, there must be 5 cats because there are twice as many dogs as cats. (Two times 5 is 10.)

Given that 10 plus 5 is 15, 10 is the correct answer. 

If half of the 6 puppies gain one pound, that means that 3 puppies will gain one pound. This means that 3 total pounds will be gained among the 6 puppies. 

We can assume that the weight of each puppy was originally 7 pounds, since the average was 7. Three of the puppies have gained a pound, meaning they will weigh 8 pounds.

Weights of the puppies after one week: 7, 7, 7, 8, 8, 8

Find the new average by summing the individual weights and dividing by the number of puppies.

$\displaystyle \frac{7+7+7+8+8+8}{6}=\frac{45}{6}=7.5$

If the original price of the shirt was $\displaystyle \$25.00$, but it is on sale for $\displaystyle 20\%$ off, then that means the shirt will be discounted by $\displaystyle \$5$ because $\displaystyle 20\%$ of $\displaystyle 25$ is $\displaystyle 5$. $\displaystyle \$25.00-\$5.00=\$20.00$. Additionally, with the $\displaystyle \$10.00$ off coupon, the final price would be $\displaystyle \$20.00-\$10.00=\$10.00$.

If Rebecca buys a $\displaystyle \$30.00$ sweater that is part of a buy one, get one free sale, that means that she will get two sweaters for a total of $\displaystyle \$30.00$. A $\displaystyle 10\%$ off discount will mean that Rebecca will save $\displaystyle \$3.00$ off of her total because $\displaystyle 10\%$ of $\displaystyle 30$ is $\displaystyle 3$.

Therefore, the total she will pay is equal to $\displaystyle \$30.00-\$3.00=\$27.00$. 

The average price of a sweater will therefore be $\displaystyle \frac{\$27.00}{2}=\$13.50$.

If $\displaystyle 70\%$ of the students in a classroom of $\displaystyle 30$ students are boys, that means that $\displaystyle 21$ students are boys, since $\displaystyle 0.70\cdot30=21$. (Alternatively, you could figure this out by realizing that since $\displaystyle 70\%$ of $\displaystyle 10$ is $\displaystyle 7$ and $\displaystyle 10\cdot3=30$, $\displaystyle 70\%$ of $\displaystyle 30$ must equal $\displaystyle 7\cdot3$, which is $\displaystyle 21$.) If there are $\displaystyle 21$ boys in the classroom, there must be $\displaystyle 9$ girls, since $\displaystyle 30-21=9$.

 Given that $\displaystyle \frac{1}{3}$ of the girls wear their hair in pigtails, and $\displaystyle \frac{1}{3}$ of $\displaystyle 9$ is $\displaystyle 3$, it follows that there are $\displaystyle 3$ girls in the classroom who wear their hair in pigtails.

The sum of $\displaystyle 36+37+38=111$ . The easiest way to discover the middle number of this set is to divide 111 by 3:

 $\displaystyle \frac{111}{3}=37$

Now that you have the middle number, simply add one to it and subtracy one from it to get your consecutive numbers:

$\displaystyle 37-1=36$

$\displaystyle 37+1=38$

If 3 brothers weigh 80 pounds, 120 pounds and 135 pounds, and the smallest brother gained 15 pounds over the past year, while the largest brother lost 5 pounds, the new weights of the brothers are:

95 pounds, 120 pounds, and 130 pounds.  (The middle brother's weight did not change.)

Given that the average is found by dividing the sum of the numbers in a list by the number of items in that list, the following equation will be used:

$\displaystyle \frac{95+120+130}{3}$

$\displaystyle \frac{345}{3}=115$

Therefore, the new average is 115 pounds. 

If 25 percent of a number is 3, then that means that 100 percent of the number will be equal to 3 times 4, which is 12. Two thirds of the number 12 is 8; therefore, 8 is the correct answer. 

Divide: $\displaystyle 357.5 \div 55= 6.5$

Answer: It will take Stephanie $\displaystyle 6.5$ hours to arrive.

Divide: $\displaystyle 18\div 6=3$

Answer: Each friend will receive $\displaystyle \$3.00$.