A young boy has 40 total pets. He has two different types of pets. He has cats and penguins. The total number of the heads of his pets plus all the wings equals the total number of feet of his pets. How many cats and how many penguins are there?

He has 30 penguins and 10 cats.

Step-by-step explanation:

Let's define the variables:

C =  number of cats.

P = number of penguins.

We know that he has a total of 40 pets, then:

C + P = 40

We also know that the total heads (40 heads, each animal has one) plus the number of wings (P*2, each penguin has 2) is equal to the number of feet of his pets (4*C + 2*P, because each cat has 4 paws, and each penguin has 2)

Then we have the equation:

40 + 2*P = 4*C + 2*P

Notice that in the second equation we have the term 2*P in both sides of the equation, then we can just subtract 2*P in both sides to get:

(40 + 2*P) - 2*P = 4*C + 2*P - 2*P

40 = 4*C

Now with this, we can find the value of C.

40/4 = C = 10

Then he has 10 cats.

Now we can replace this in the equation:

P + C = 40

to find the value of P

P + 10 = 40

P = 40 - 10 = 30

P = 30

He has 30 penguins.

65

step-by-step explanation:

3< x< 5

step-by-step explanation:

|x - 4| < 1

there are two solutions, one positive and one negative.   remember to flip the inequality when taking the negative solution

x-4 < 1       x-4 > -1

add 4 to each side

x-4+4 < 1+4       x-4+4 > -1+4

x< 5                 x> 3

3< x< 5