BTGmoderatorLU wrote: ↑Mon Aug 03, 2020 6:58 am

**Source: GMAT Paper Tests**
A salesman makes a 20 percent commission on the selling price of each set of encyclopedias he sells. If he sells 12 identical sets of encyclopedias and makes $1800 in commissions, what is the selling price of the each set?

A. $300

B. $600

C. $750

D. $900

E. $1080

The OA is

C

Let x = the selling price of ONE set of encyclopedias

So,

12x = the TOTAL price of 12 sets of encyclopedias

If the commission is 20%, then the salesman's commission = 20% of

12x
If the salesmen receives $1800 in commissions, we can write: 20% of

12x = $1800

Rewrite as: (0.2)(12x) = $1800

**We COULD evaluate (0.2)(12) to get 2.4, but I'd rather not have to divide 1800 by 2.4**

Instead, here's what I'd do to speed up the calculations (in my head).
Take: (0.2)(12x) = $1800

Divide both sides by 12 to get: (0.2)(x) = $150

Rewrite 0.2 as 1/5 to get: (1/5)x = $150

Multiply both sides by 5 to get: x = $750

Answer: C

Cheers,

Brent