Here, Sequence : -2, -6, -18, -54
Common Ratio = a₂/a₁ = -6/-2 = 3
As the expression is in negative sign, it's sequence will be -3ˣ
Where x = number of terms in the sequence [ By this rule, you can calculate the unknown nth number]
In short, Option C is your answer!!!!
Let me know, if you have some doubt.
Odd numbers take the form
, where
is an integer. When
, the last odd number would be 799. So we're adding

By reversing the order of terms, we have

and we can pair up terms in both sums at the same position to write

so that we are basically adding 400 copies of 800, and from there we can find the value of the sum right away:

###
We could also make use of the formulas,


We have

5 is the answer to the promblem
PQ would be 4 square root 6 times square root of 2, which is also 4 square root 12. Simplified, it would be 8 square root 3
Answer:
the answer to - 2/5 -4/5 + - 9/10 is -2.1