Try This

[fudgefudge]

1+4= 5 2+5=12 3+6=21 5+11= ?

[fiction-factory]

49

[hc4361]

37

[fiction-factory]

oops didn't spot you'd missed 4 out
60

[fiction-factory]

1+ 1x4 =4
2+ 2x5 =12
3+ 3x6 =21

5+ 5x11= 60

Not sure why the number 11 is in the pattern though- would have expected it to have been 8

[Togo]

1 + 4(x1)=5
2 + 5(x2)=12
3 + 6(x3)=21
5 + 11(x4)= 49

[rockyracoon]

37. Is there more than one possible answer?

[fudgefudge]

not sure of answer

[fiction-factory]

Where did the puzzle come from please fudgefudge?

[Quizproquo]

1+ 4x1 = 5
2+ 5x2 = 12
3+ 6x3 = 21
5+ 11x5 = 60

[Baldric]

If you're not sure of the answer (@ 1005) what's the point?

[Baldric]

Was it meant to be this one, which has 8 + 11 not 5 + 11 as last part?

http://www.telegraph.co.uk/education/2016/04/22/this-maths-problem-has-thousands-of-people-baffled-can-you-work/

[fiction-factory]

Probably should be that as there is no fully logical pattern to all the numbers as shown above.
8+ 8x11= 96

[Togo]

Lol fudge not only did you not know the answer......you got the question wrong. It looks as if it should have read 8 + 11=?, as in Baldrics link. There are two answers therefor. Either 40 or 96 depending on how you look at the progression.

[Old_Geezer]

I don't think there is enough info

5 in base 6 (or above) = 5
7 in base 5 = 12
9 in base 4 = 21
16 in base 3 would = 51

[Togo]

To arrive at 40 just add the answer to the first addition to the next. ie

1+4=5
2+5(+5)=12
3+6(+12)=21
8+11(+21)=40
ff has given the way to get 96

[fiction-factory]

Have we amended the question correctly now fudgefudge (see Baldric's post) and our revised answer of 96?

[sillysally5]

Answer is 37
1+4=5
5 +2+5=12
12+3+6=21
21+5+11=37

[Baldric]

thank goodness you turned up SillySally

[hc4361]

Hurrah! I was right :D

[fudgefudge]

came off facebook= no answer