Which of the following equations is an example of direct variation?
y + 10 = 2(x + 5)
y = 2(x + 5)
y + 5 = 2(x + 5)
y = x + 5
!

Direct variation is when  x/y = constans 
That's mean, that   formula of direct variation is y=kx   (k inequal 0)

First:
y+10=2(x+5)
y+10 = 2*x + 2*5
y+10=2x+10     /subtract 10 
y=2x  
It is  y=kx.  Here  k=2   -  it is example of direct variation.

Next:
y=2(x+5)
y=2*x + 2*5
y=2x+10
It is not  y=kx  (because you've got +10). So it isn't. 

Next:
y+5=2(x+5)
y+5=2x+10   /subtract 5
y=2x+5
It isn;t too, because you've got  +5.

Next:
y=x+5   isn't, because you've got +5. 

So only first equation

60

Step-by-step explanation:

Use r-combinations.

Treat it as though u are filling in 6 slots

_ _ _ _ _ _

1. First fill in the 7s, there are three of them and 6 ways to do so

so (6 Choose 3)

2. then fill in the 2s, now with the 3 slots taken up by the 7, 3 slots left.

So its (3 Choose 2).

3. and only 1 way to fill in the 8. (1 choose 1)

By multiplicative rule,

(6C3) * (3C2) * (1C1) = 60