1,3,5
2,4,?
Answer:
Difference between numbers is 2 so 6 can replace ? mark.
Sum first two digits and add first digits. (1+3)+1=5 then (2+4)+1=7. so 7 can replace ? mark.
Sum first two digits and multiply 2 and minus second one: (1+3)x2-3=5 then (2+4)x2-4=8. So 8 is ok too.
Multiply first digit with 8 then minus second digit: 8×1-3=5 then 8×2-4=12. So 12 is ok too,
But for 11??. Answer should be d)11 can not replace question mark.
Brain Teaser Questions 