Four digit so : -- -- -- --

First one prime number so : 2 3 5 7 : 4 chance
Second number : 0-9 : 10 chnace
Third number : 2 3 5 7 : 4 chance
fourth number : 0 or 5 : 2 chance

so 4*10*4*2 = 320

Take the task of creating 4-digit numbers and break it into stages.

Stage 1: Select a digit for the 1st position (i.e., the thousands digit)
This digit must be PRIME, which means it can be 2, 3, 5, or 7
So, we can complete stage 1 in 4 ways

Stage 2: Select a digit for the 2nd position (i.e., the hundreds digit)
There are no restrictions for this digit, so we can choose any digit from 0 to 9
We can complete stage 2 in 10 ways

Stage 3: Select a digit for the 3rd position (i.e., the tens digit)
This digit must be PRIME, which means it can be 2, 3, 5, or 7
So, we can complete stage 3 in 4 ways

Stage 4: Select a digit for the 4th position (i.e., the unit digit)
Since the resulting 4-digit number must be divisible by 5, we know that the unit's digit must be either 0 or 5
So we can complete stage 4 in 2 ways

By the Fundamental Counting Principle (FCP), we can complete all 4 stages (and thus create a 4-digit number) in (4)(10)(4)(2) ways (= 320 ways)

Answer: C

Note: the FCP can be used to solve the MAJORITY of counting questions on the GMAT. So, be sure to learn it.

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