## April 20, 2010

### Solve 2 3 4 15 12 3 4 5 28 20 4 5 6 45 30 5 6 7 66 42 6 7 8 ? 56

Find the missing number ?

2 . 3 . 4 . 15 . 12
3 . 4 . 5 . 28 . 20
4 . 5 . 6 . 45 . 30
5 . 6 . 7 . 66 . 42
6 . 7 . 8 . ?? . 56

karthik said...

91 is the missing number
4*3+3*1=15
5*4+4*2=28
6*5+5*3=45
7*6+6*4=66
8*7+7*5=91

Pierce said...
This comment has been removed by the author.
Pierce said...

I also got 91 but through a different, but similar, method (i utilize the first four columns of numbers only):

2+ 3*4 + 1 =15
3+ 4*5 + (1)+4 =28
4+ 5*6 + (5)+6 =45
5+ 6*7 + (11)+8 =66
6+ 7*8 + (19)+10 =91

Pierce said...

Karthik's is more elegant, darn it

Suresh Kumar N. said...

2 . 3 . 4 . 3*5=15 . 3*4=12
3 . 4 . 5 . 4*7=28 . 4*5=20
4 . 5 . 6 . 5*9=45 . 5*6=30
5 . 6 . 7 . 6*11=66. 6*7=42
6 . 7 . 8 . 7*13=91. 7*8=56

anonymous said...
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anonymous said...
This comment has been removed by the author.
Randy said...

I agree with Kuresh. The math is there.
R.

Nithya said...

A B C((B*C)+(B*(A -1)))(B*C)
2 3 4 ( 12 + 3 *1) 12
3 4 5 (20 + 4 * 2) 20
4 5 6 (30 + 5 * 3) 30
5 6 7 (42 + 6 * 4 ) 42
6 7 8 (56 + 7 * 5 ) 56

I arrived 91

Pratap said...

I too got 91.

A B C ((A+B)*(C-1)) (B*C)
2 3 4 15 12
.
.
.
.
6 7 8 ((6+7)*7=91)

Kevin said...

Ali said...

I got the same but through different method,
(first number +third number - 1) * second number
(2+4-1)*3=15
(3+5-1)*4=28
(4+6-1)*5=45
(5+7-1)*6=66
(6+8-1)*7=91

Active King said...

I too got 91..
col 3 col 4
(4*3) +3 = 15
(5*5) +3 = 28
.
.
.
.
(8*11) +3 = 91

Ólafur said...
This comment has been removed by the author.
Ólafur said...

A B C D E
D=((A+B)*C)-(A+B))
E=B*C

Value of E is immaterial and the missing D=91

Anonymous said...

I went a completely different way but still got 91.

Pattern in column 1 is +1
pattern in column 2 is also +1
Column 3 starts at +13, adding an extra 4 per row.
eg. 15+13 = 28
28+13+4=45
45+13+4+4=66
66+13+4+4=91

Anonymous said...

91

Babu vincent said...

91

n1*n2 ^ 2 + (n3-1)

Anonymous said...

91

Anonymous said...

(a + b) * b
(6 + 7) * 7 = 91

yuvraj said...

in 4 th row ..see the diff between numbers
28-15=13
45-28=17
66-45=21
??-66=25

ans.91

yuvraj said...

in 4 th column ..see the diff between numbers
28-15=13
45-28=17
66-45=21
??-66=25

ans.91

Hrishi said...

91

Jeevan Patil said...

((2+3)*(4-1))=15
((3+4)*(5-1))=28
((4+5)*(6-1))=45
((5+6)*(7-1))=66
((6+7)*(8-1))=91

jeevanrocks19@gmail.com said...

((2+3)*(4-1))=15
((3+4)*(5-1))=28
((4+5)*(6-1))=45
((5+6)*(7-1))=66
((6+7)*(8-1))=91

jeevanrocks19@gmail.com said...

((2+3)*(4-1))=15
((3+4)*(5-1))=28
((4+5)*(6-1))=45
((5+6)*(7-1))=66
((6+7)*(8-1))=91

jeevanrocks19@gmail.com said...

((2+3)*(4-1))=15
((3+4)*(5-1))=28
((4+5)*(6-1))=45
((5+6)*(7-1))=66
((6+7)*(8-1))=91

jeevanrocks19@gmail.com said...

((2+3)*(4-1))=15
((3+4)*(5-1))=28
((4+5)*(6-1))=45
((5+6)*(7-1))=66
((6+7)*(8-1))=91

jeevanrocks19@gmail.com said...

((2+3)*(4-1))=15
((3+4)*(5-1))=28
((4+5)*(6-1))=45
((5+6)*(7-1))=66
((6+7)*(8-1))=91

Anonymous said...

Was I the only one who used fractions?

The last colum going down, ratios are:
12/20 => 20 = 12 + 8 = (1+2/3)*12
20/30 => 30 = 20 +10 = (1+2/4)*20
30/42 => 42 = 30 +12 = (1+2/5)*30
... = (1+2/6)*42
This gave me the idea for the diaganol.
ratios:
12/28 => 28 = (2 + 1/3)*12
20/45 => 45 = (2 + 1/4)*20
... = (2 + 1/5)
... = (2 + 1/6)*42
= 84 + 7 = 91

M. Roy said...

OK, I'll probably go when I get the answer... but this one is bugging me... the Meme reads "Only For Geniuses" and then gives the following pattern:

1 + 4 = 5
2 + 5 = 12
3 + 6 = 21
8 + 11 = ?

The two answers that have been given are 39 and 96