Total Number of Stores = 181 * 113

Total Number of Products sold = 181 * 113 * 51752

= 1.81 * 10^2 * 1.13 * 10^2 * 5.1752 * 10^4
=1.8*1.1*5.17 * 10^8

Approx = 2*1*5 * 10^8 = 10*10^8= 10^9

D

51752*181*113 or
51000*180*113 or
50000*200*100
=10^9

hope it helps

We are given that a certain manufacturer sells its products to stores in 113 different regions, with an average (arithmetic mean) of 181 stores per region and 51,752 units per store.

Since we are asked, which of the following is closest to the total number of units of manufacturer’s product sold worldwide last year, we can use estimation.

113 ≈ 100

181 ≈ 200

51,752 ≈ 50,000

Thus, the approximate number of units sold worldwide last year was:
100 x 200 x 50,000 = 1,000,000,000 = 10^9

Answer: D
_________________

1. 181 Stores x 113 regions = 20,453
2. 20,453 x 51,752 (I worked this out the long way but scientific notation is faster)
3. 2 x 10^4 x 5 x 10^4 = 10 x 10^8 (just add exponents since base and exponent is the same)
4. 10^9

Answer (D)

how do we know what is the correct level of approximation ?

I tried

180 * 110 * 52000 = which gives a 10^8
why cant this be the answer ?
Bunuel can you please tell me how much of an approximation is correct on the gmat ?