Thread: Missing number in the series

What is the missing number in the series?
4,9,20,43,90??

Ans: 185.

diff between 4 and 9 is 5 (4+1)
diff between 9 and 20 is 11 (9+2)
diff between 20 and 43 is 23 (20+3)
diff between 43 and 90 is 47(43+4)


-- James

James your approach is prefect and the solution for this problem is 185 as you found out.

Originally Posted by scott

What is the missing number in the series?
4,9,20,43,90??

Another approach

(4*2) + 1 = 9
(9*2) + 2 = 20
(20*2) + 3 = 43
(43*2) + 4 = 90
(90*2) + 5 = 185

yep

current No - (90 + 5)

Prev No - 90

so 90 + 95 = 185

Originally Posted by scott

What is the missing number in the series?
4,9,20,43,90??

the last no of the series is 143

4 9 20 43 90 ?

the difference

4 9 20 43 90 ?

5 11 23 47 ?

6 12 24 48

so the 3rd series is 6 12 24 (48) it doubles the digit.. adding 48 in 47 so the figure is 95 now we got main difference series.....adding 95 in main series 90 then ans is 185.

Hi,

The missing number is 185.

Here is the explanation

4 9 20 43 90

9-4=5
20-9=11
43-20=23
90-43=47

(5*2)+1=11
(11*2)+1=23
(23*2)+1=47

so, in the same way (47*2)+1=95

So, x-95=90.

Therefore x= 185.

Thanks

Originally Posted by scott

What is the missing number in the series?
4,9,20,43,90??

please find the steps

answer is 186

answer is 186&379

How can I draw up a formula that number series?

4,9,20,43,90??

Thank you!

Hi Isabele,

The formula is defined as
The difference between 9-4= 4+1 is 5
20-9=(5+5)+1 is 11
43-20=(11+11)+1 is 23
90-43=(23+23)+1 is 47
185-90=(47+47)+1 is 95
so the answer is 90+95(add last number+difference number) = 185

4 + 4 + 1 = 9
9 + 9 + 2 = 20
20 + 20 + 3 = 43
43 + 43 + 4 = 90
90 + 90 + 5 = 185

185
In this series each 2nd no is incremented by 1 with double of the previous number.
9=4*2+1
20=9*2+2
43=20*2+3
90=43*2+4
so, next number will be 185 as
185=90*2+5