How many two digit numbers are there such that the product of their digits after reducing it to the smallest form is a prime number? for example if we take 98 then 9*8=72, 72=7*2=14, 14=1*4=4. Consider only 4 prime no.s (2,3,5,7)  Choose the correct choice from the following answers.
A) 16	B) 17	C) 18	D) 19	E) 20
we know prime no. are 2 ,3 , 5, 7   mulply by 1 is prime no   2 = 21(2*1)=73(7*3)   2 = 21 (2*1)=37(3*7)   2= 12(1*2)=43(4*3)or34(3*4)   or26(2*6)or62(6*2)   .   .   .similarly for all prime no then u will got it....   12,13,15,17,21,26,31,34,35,37,43,51,53,57,62,71,73,75   ans is 18   ANSWER:18
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How many two digit numbers are there such that the product of their digits after reducing it to the smallest form is a prime number? for example if we take 98 then 9*8=72, 72=7*2=14, 14=1*4=4. Consider only 4 prime no.s (2,3,5,7)