# Is it possible to find out the value of given variable in the following question?

It is given that $u_1 = 1, u_2+u_3 = 6$ and $u_4+u_5+u_6+u_7+u_8 = 30$. What is the approximate value of $u_4$ when computed by using Lagrange's interpolation formula?

1) $7$

2) $6$

3) $5$

4) $4$

• The question is written pretty poorly. Is $u_i$ the value of a function at $x=i$? Perhaps there is context that we are missing. – parsiad Mar 26 '17 at 13:20
• That doesn't sound like a normal interpolation problem; ordinarily you would be given exact values of $u$ at each of several values of $x$ and then interpolate them from there. – Ian Mar 26 '17 at 13:20