GMAT Math

Can anyone provide an explanation for the following problems?

A committee of 3 people is to be chosen from 4 married couples. What is the number of different committees that can be chosen if 2 people who are married to each other cannot both serve on the committee?


In the xy-plane, what is the y-intercept of line l?

(1) slope of line l is 3 times its y intercept
(2) x intercept of line l is -1/3


When a tree was first planted, at 4 feet tall. The tree's height increases constantly each year for 6 years. At the end of the 6th year, the tree was 1/5 taller than at the end of the 4th year. What was the constant increase per year in feet?

3/10, 2/5, 1/2, 2/3, 6/5

1st Question
https://www.beatthegmat.com/permutation- ... 21950.html

3rd Question
https://www.beatthegmat.com/translating- ... 39765.html

2nd question

ans E)

remember that equation of a line y=mx+c, where m is the slope, C is the y intercept.

S1. slope of line l is 3 times its y intercept
this tell us that m=3c, but nothing else, insuff

S2. x intercept of line l is -1/3
this tell us that 0=m(-1/3)+c, dunno m so we don't know what c is, insuff

both combined
substitute m=3c in 0=m(-1/3)+c,
we get
0=3c(-1/3)+c
0=-c+c,
this does not tell us anything about the c or m, insuff.

therefore ans is E)... I think

Hope this helps, it will be a good idea to do forum search for the questions before creating a thread about it.

will do...thanks for your help

(1)
(8 x 6 x 4) / 3
64

(2)
y = ax + b
y = (3b)x + b
-1/3 = (3b)0 + b
-1/3 = b
y = -x - 1/3
slope = -1

(3)
start = 4
end year 1 = 4 + x
end year 2 = 4 + 2x
end year 4 = 4 + 4x
end year 6 = 4 + 6x
(4 + 4x)(6/5) = (4 + 6x)
24 + 24x = 20 + 30x
x = 2/3