Question

21:145::13:962::61:257::51:?

Answer 1

the (+ve) and (- ve) sign of the numbers is important.........as it can change the answer by just changing the sign.....

Answer 2

The missing term in 21:145::13:962::61:257::51:? is 226

Solution:

Given, set of ratios are 21 : 145 :: 13 :  962 :: 61 : 257 :: 51 : ?

We have to find the missing term.

Now, second term in each individual ratio is obtained by reversing the digits of first number and adding 1 to the square of reversed digits.

$\begin{array}{l}{21: 145 \rightarrow 12^{2}+1=144+1=145} \\ {13: 962 \rightarrow 31^{2}+1=961+1=962} \\ {61: 257 \rightarrow 16^{2}+1=256+1=257}\end{array}$

So, now

$51: ? \rightarrow 15^{2}+1=225+1=226$

Hence, the missing term is 226.