Got it. Although I'll post my answer later, to avoid spoiling the fun for others.

I think 90

Soooo, following bob_cville, should we not post our answers?

I got 90. But my answer may or may not be correct.

Got it as well. Agreeing with 90.

Maybe 54???

Do over....do over.
I think it's 9 x 10 = 90

Another 90. But I didn't get it by multiplying 9 by 10. All sorts of ways to do a math problem. :-)

I got 90 too. I think I also see the way alisande got the answer

like others here I did 9 * 10 to get 90

the other way would be to do: 9 * 9 + 9 = 90

or in general X * (X+1) == (X * X )+ (X * 1) == (X * X) + X

o j, O.K? ... and not about to say, O.L., even if I turn out to be in error

I agree with joyful....72

72 and it's a fractional answer.

I go with 90

or 110

If you look at it like a puzzle the left side goes up by ones but the right side goes up by 2's. (6, 8, 10, 12...)

just sayin'

This post was edited by blfenton on Thu, Apr 24, 14 at 20:51

72

Sue

The answer I got is 90, although admittedly I'm mathematically impaired! I calculated - 2 (x 3) = 6; 3 (x 4) = 12; 4 (x 5) = 20; 5 (x 6) = 30; 6 (x 7) = 42; [7 x 8 = 56; 8 x 9 = 72]; 9 (x 10) = 90.

Each number in the left column is multiplied by numbers increasing by one for every subsequent left column number. The answers for the missing 7 and 8 on the left have to be inferred.

I get 90 by the same reason as poster Stacey above. (I came to that conclusion before I looked at the replies.)

72 here.

Yep - 72.

72 here

Definitely 90. I think. Ha!

Would those who said 72 please explain how? I am wondering.

Okay,now I understand how it is 90

2x3=6. 3x4=12 etc so it's 9 x 10 =90

Each one is a series of a number multiplied ny the next higher number!!

2 x 3 = 6
3 x 4 = 12
4 x 5 = 20
5 x 6 = 30
6 x 7 = 42
7 x 8 = 56
8 x 9 = (72)
Second number increases by one each time ... stays one ahead of the first number.

o j, O.K ... and, again, not about to say, "O L" if I turn out to be in error

Sorry about the error - I'd previewed, so couldn't check back after 6, then the original skipped the 7 and 8 in the sequence, going to 9, and I assumed that the hidden number following the 9 was 8, to multiply to 72.
____________________________

Still wrong - I'd assumed that the hidden number was one above the one shown in each case ...

... but then when I got to 9, instead of considering the hidden number to be one above, which would make the answer "90" ... I assumed that the hidden number was one below the visible one, to provide 72.

So ... can I change my reply?

How about 90, which most folks said?

And can I also, in spite of what I claimed, say, "O.L."?

ole joyful ... wrong - again! Oh, well - no one wins 'em all!