CTET PAPER I 2019 · PYQ · Number System / Prime Numbers · medium
I am a 2 digit number. The digit in tens place and the digit in units place are consecutive prime numbers. The sum of digits is multiple of 3 and 4. The number is
A.57✓ Correct
B.23
C.35
D.13
Explanation
Consecutive primes that could form a two-digit number: (2,3), (3,5), (5,7), (7,11)... Check sums: 2+3=5, 3+5=8, 5+7=12. The sum must be a multiple of both 3 and 4, i.e., multiple of 12. Only 5+7=12 satisfies this. So digits are 5 and 7. The number is 57 (with 5 in tens place and 7 in units place; both are consecutive primes).
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