[問題]天山4-Q32

[balanana]

Q32:
If n is an integer between 10 and 99, is n < 80 ?
(1)The sum of the two digits of n is a prime number.
(2)Each of the two digits of n is a prime number.

Ans: B

條件1:
12,21,14,41,16,61,29,92,49,94,...所以不充分~
條件2:
27,72,23,32...所以不充分~

請問答案B怎麼算出來得呀???

[lance921]

因為十位數一定小於8
所以可推知n小於80