Question

1) After giving $5 to Greg, David has $25. Greg now has 1/5 as much as Davis does. How much did Greg start with?

2) if 3a+4b=4a-4b=21 find the value of a
A)3
B)6
C)21
D)42
E) the answer can not be determined from the information given

^ i think it’s C?

3) If N is a positive integer, which of the following does not have to be a divisor of the sum of N,6N, and 9N?
A)
B)2
C)4
D)9
E)16
^Is it D??

Answer 1

1) So Greg has 1/5 of 25, so he has $5. He was given $5 in the beginning, so at first he had 5-5=0 dollars

2) Subtract 3a from each side, ignoring the 21 for now:
4b=a-4b

Add 4b to each side
8b=a

Going back to the first equation, we have
3a+4b=21
Since a=8b, we can substitute
3(8b)+4b=21
24b+4b=21
28b=21
b=21/28=3/4
so b=3/4 and a=8b
8*b=8*3/4=24/4=6
answer is B

Answer 2

3)
N+6N+9N=16N
All the factors of 16 must be a factor of 16N, so 1, 2, 4, 8, and 16 are all factors. 9 does not have to be a factor, answer is D) 9