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Answer: 9
2 __, 4 __, 6 __, 8 __
reverse even
1 __
11: reverse 11
13: reverse 31
15 not prime
17: reverse 71
19: reverse 91 = 7$\times$13
31: already counted as 13
33, 35 not prime
37: reverse 73
39 not prime
5 __ reverse multiples of 5
77 not prime
79: reverse 97
9 __ already counted via reverse (except for 99, not prime)
5 ticks which are 4 pairs plus 11
Total 9
Reversible Primes
Age 11 to 14
ShortChallenge Level 
Answer: 9
2 __, 4 __, 6 __, 8 __
reverse even1 __
11: reverse 11
13: reverse 31
15 not prime
17: reverse 71
19: reverse 91 = 7$\times$13
31: already counted as 13
33, 35 not prime
37: reverse 73
39 not prime
5 __
reverse multiples of 577 not prime
79: reverse 97
9 __ already counted via reverse (except for 99, not prime)
5 ticks which are 4 pairs plus 11
Total 9
You can find more short problems, arranged by curriculum topic, in our short problems collection.
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