Latest Elitmus Aptitude Question SOLUTION: 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=1

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(#M40154156) ELITMUS Numerical Ability question Number System (Asked on 18-10-2015) Keep an EYE

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)

Asked In Elitmus Vishal kungwani (8 years ago)

Solved richa Read Solution (10)

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richa  (8 years ago) Best Solution

answer is 18

bcs
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

Is this solution Helpfull? Yes (49) | No (3)  

jitendra kumar kewat  (8 years ago)

(this one is 100% right)Explanation:
2 = 12 or 21 So 1×2, 2×1, 3×4, 4×3, 2×6, 6×2, 3×7, 7×3
3 = 13 or 31 So 1×3, 3×1
5 = 15, 51 So 1×5, 5×1, 3×5, 5×3, 7×5, 5×7
7 = 17 or 71 So 1×7, 7×1
15 = 3×5 = 5×3
So total 18 numbers = 12,13,15,17,21,26,31,34,35,37,43,51,53,57,62,71,73,75
so Ans is >>18

Is this solution Helpfull? Yes (15) | No   

Akshay  (8 years ago)

answer is 18
ans the numbers are
12
13
15
17
21
26
31
34
35
37
43
51
53
57
62
71
73
75

Is this solution Helpfull? Yes (3) | No (1)  

shubham gupta  (8 years ago)

answer is 16

bcs
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)
.
.
.similarly for all prime no then u will got it....


43 , 34 , 57 , 75 , 53 , 35 ,12,13,15,17,37,73,21,31,51,71

ans is 16 no . only satisfy yhe condition

Is this solution Helpfull? Yes (1) | No (8)  

Anuj singla  (8 years ago)

ans is only 18

Is this solution Helpfull? Yes (1) | No   

ashish sahu  (8 years ago)

24 is the right ans

Is this solution Helpfull? Yes (1) | No (9)  

Vishal kungwani  (8 years ago)

@shubham i also got 16 but 16 was not in the options. Options were 10,14,18 and 24

Is this solution Helpfull? Yes | No   

DHEERAJ KUMAR  (8 years ago)

ans is 18.for those who are getting 16 please recheck

Is this solution Helpfull? Yes | No   

priyanka  (8 years ago)

Can someone please tell that why we are not considering 14(1*4=4 = 2^2,18=2^3,19 =3^2)..

Is this solution Helpfull? Yes | No (2)  

Jay singh  (8 years ago)

15+51=66
66+66=132
132+321=363
363+363=726
726+627=1353

Is this solution Helpfull? Yes | No (2)  

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