3x + 4y = 31
2x - 4y = -6
*The +4 and -4 in the center of the equation cancel out because 4-4 = 0*
3x = 31
2x = -6
------------
*add like terms*
3x + 2x = 5x
31 - 6 = 25
So now you should have this written on your paper ... > 5x = 25
*Divide by 5 on each side*
5x = 25
_ _
5 5
x = 5
C
Because 1 km is 1,000 meters so you were just multiply 1000 by 10 and get 10,000
c:
If Bob can paint the fence in 4 hours, then in 1 hour he gets 1/4 of the fence painted. If Sarah can paint the fence in 2.5 hours, then she gets 2/5 of the fence painted in one hour (1/2.5 = 2/5). We add those amounts together and set them equal to 1/x, x being the the total time it will take them to paint the whole fence. 1/4 + 2/5 = 1/x. Find a common denominator first, then add the left side together. 5/20 + 8/20 = 1/x. 13/20 = 1/x. Cross-multiply to get 13x = 20 and x = 1.54 hours, just a bit over an hour and a half.
For the first question the problem is simple. He is essentially going around 2 sides of a triangle, instead of along the hypotenuse. You would have to use Pythagoras' theorem for the real answer, a^2 + b^2 = c^2. However, for question 15, i don't know, I'm pretty sure this is an American question and I'm British, I don't believe I have ever encountered ordered pairs, or at least i don't remember learning them. Hope this helps ;)
