The phrase "approximating the number of" is correct and usable in written English.
You can use it when discussing estimates or calculations related to quantities or figures.
Example: "The study focused on approximating the number of species in the region based on available data."
Alternatives: "estimating the quantity of" or "calculating the total of".
One simple and practical method from the first class consists of approximating the number of modules in a protein as the number of regular secondary structure elements (i.e., helices and sheets).
The channel quality is determined by calculating for each node the probability to access the channel in a distributed manner by approximating the number of successful and failed transmissions.
Most strikingly, BCIA simulations of networks with large but bounded numbers (109 1013) of nodes, approximating the number of neurons in the human brain, found that the length of simulated signaling pathway can be substantially shorter than that predicted by the best known asymptotic theoretical bound in small-world networks of infinite size.
Again, we use the infinite server queue (G/G/∞) as a basis for approximating the number of occupied hospital beds.
The possibility of using a straight line for approximating "the number of longevity SNPs -- life span" relationship indicates the presence of substantial additive component of the genetic contribution to longevity.
An alternative method for approximating the number of inputs to a cell originally introduced to quantify number of inputs at the retinogeniculate synapse (Hooks and Chen, 2006), uses the SF current(s) recorded in a cell as the estimate of mean input strength.
In the simulation presently employed, 48 chromosomes carried the selected mutation (derived) and 48 chromosomes did not (ancestral), approximating the numbers of individuals we examined in each population.
The 1,600 shown on your map as the size of the Colonial Army approximates the number of Washington's troops that were on Chatterton Hill, where the major engagement took place.
In Eq. 22, (sum _{l ne k} left( {1 - p_{l} } right)) approximates the number of products in the demand mood and (sum _{l ne k} left( {p_{l} } right)) approximates the number of products in the production mood.
The fundamental vibration period of an RC building has the range shown in Eq. (2), which approximates the number of stories in the building.
In order to implement such a solution, one needs to keep a counter that approximates the number of current TCP flows in each dynamic wireless node.
