If each of the letters in the English alphabet is assigned an even numerical value according to $\text{A}=2,\text{B}=4,\text{C}=6,\dots ,\text{Z}=52$, then what will be the total value of the letters for the word 'PHOTOSYNTHESIS'?

The numerical value assigned to each letter is exactly twice its standard alphabetical rank ($\text{Value}=2\times \text{Rank}$).
Let's find the standard ranks for the letters in $\text{’PHOTOSYNTHESIS’}$ and sum them up:

$$\text{P}=16,\text{H}=8,\text{O}=15,\text{T}=20,\text{O}=15,\text{S}=19,\text{Y}=25,\text{N}=14,\text{T}=20,\text{H}=8,\text{E}=5,\text{S}=19,\text{I}=9,\text{S}=19$$

$$\text{Sum of standard ranks}=16+8+15+20+15+19+25+14+20+8+5+19+9+19=212$$

Since each letter value is doubled:

$$\text{Total Value}=2\times 212=424$$

Therefore, the total value is $424$.