Find the area of the quadrilateral of one of its diagonals is 20 cm and its off sets 9 cm and 6 cm?
Options:
(A) 128
(B) 150
(C) 887
(D) 279
(E) 771

1/2 * 20(9 + 6) = 150 cm2 So the answer is: (B).

A can do a job in 18 days and B can do it in 30 days. A and B working together will finish twice the amount of work in ------- days?
Options:
(A) 21 ½ days
(B) 22 ½ days
(C) 23 ½ days
(D) 12 ½ days
(E) none of these

1/18 + 1/30 = 8/90 = 4/45
45/4 = 11 ¼ *2 = 22 ½ days So the answer is: (B).

The inverse ratio of 3: 6: 1 is?
Options:
(A) 2:3:7
(B) 2:3:9
(C) 2:1:6
(D) 2:3:6
(E) 2:3:1

1/3: 1/6: 1/1 = 2:1:6 So the answer is: (C).

What is the units digit of the expression 14^7−17^4?
Options:
(A)  0
(B)  3
(C)  4
(D)  8
(E)  6

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
I think answer on this one should be D too. Since we know that 14^7>17^4, as Will said one should always check if the number is positive. So the answer is: (D).