How do you obtain the ppm of K+ in blood?

Question

A 0.20mL sample of blood after dilution gave an emission reading of 27. Solution B and C, containing the same amount of blood plus 50 and 100ppm of K+, respectively, gave reading of 39 and 51. Calculate the ppm of K+ in the blood sample.

Answer 1

(x+50)/(x+100) = 39/51 = 13/17

or 17x + 850 = 13x + 1300
or 4x = 450
or x = 112.5

Thus K+ conc is 112.5 ppm.

Answer 2

The reading is directly proportional to the amount of K+ present. Let the amount of K+ in blood be x.
From the given conditions,
x/x+50=27/39
Solving we get x=11.25

So the amount of K+ in blood is 11.25ppm.