question:What is the sum of all 5 digit numbers which can be formed with the digits 0,1,2,3,4 without repetation?
Options:
(A) 2599980
(B) 235500
(C) 923580
(D) 765432
(E) 765434
answer:(A)
Stream of consciousness:10(11111)*4! - 10(1111)3! = 2599980

question:A train 120 m long running at 60 kmph crosses a platform in 35 sec. What is the length of the platform?
Options:
(A) 338
(B) 277
(C) 463
(D) 456
(E) 271
answer:(C)
Stream of consciousness:D = 60 * 5/18 = 35 = 583 120 = 463

question:How many positive four-digit integers do not contain any digits other than 1 or 0 and are such that the sum of the first two digits equals the sum of the last two digits?
Options:
(A) 3
(B) 4
(C) 8
(D) 10
(E) 12
answer:
(A)
Stream of consciousness:The sum of the first two (last two) digits cannot be 0 because 0000 is not a four-digit integer. If the sum of the first two digits is 1, two variants are possible: 1001 and 1010 (we have to remember that 0 cannot be the first digit). If the sum of the first two digits is 2, one variant is possible: 1111. In all, there are three numbers that satisfy the given conditions: 1001, 1010, and 1111.