*p=p!; therefore *7=7!=5040; *7+3=5043 which is divisible by 3 hence not prime,RadiumBall wrote:For any integer p, *p is equal to the product of all the integers between 1 and p, inclusive. How many prime numbers are there between *7 + 3 and *7 + 7, inclusive?
(A) None
(B) One
(C) Two
(D) Three
(E) Four
rohu27 wrote:thrs a similar gmat prep or og prb i remember.
Q asks number of primes betwn 7!+3 and 7!+7
7!+3=3[(1*2*4*5*6*7)+1]
similarly all others can be re written as multiples of 4,5,6 and 7
as we can see each is a multiple of some number it cannot be a prime.
as its 7! we can even calculate 7! but the above method is useful for higher factorials.
This is the shortcut...rohu27 wrote: Q asks number of primes betwn 7!+3 and 7!+7
7!+3=3[(1*2*4*5*6*7)+1]
similarly all others can be re written as multiples of 4,5,6 and 7
as we can see each is a multiple of some number it cannot be a prime.
as its 7! we can even calculate 7! but the above method is useful for higher factorials.
If you add two multiples of any given number X, that sum will be divisible by X.Strongt wrote:I can find the answer by doing all the calculations, but this will take forever. Is there a shortcut for this type of questions?
