# Question #2766f

Jan 30, 2015

There are 5.25 × 10⁷ cells/mL in the original sample.

Step 1. Find the volume of a box.

I assume that the depth of the box is 0.1 mm. Then

$V = A h = \frac{1}{25} \text{mm"^2 × 0.1 " mm" = 4× 10^-3 "mm"^3 = 4 × 10^-6 "mL}$

Note: 1 mL = 1 cm³ = 1000 mm³.

Step 2. Calculate the concentration of cells in a box.

$\text{Concentration" = "cells"/"millilitres" = "7 cells"/( 4 × 10^-6"mL") = 1.75 × 10^6"cells/mL}$

Step 3. Correct for the dilution factor (DF).

Your original sample was 30 times more concentrated (DF = 30).

Original concentration = DF × concentration in slide box = 30 × 1.75 × 10⁶ cells/mL = 5.25 × 10⁷ cells/mL

The original sample contained 5.25 × 10⁷ cells/mL.