Kim is a medical supplies salesperson. Each month she receives a 5% commission on all her sales of medical supplies up to $20,000 and 8.5% on her total sales over $20,000. Her total commission for May was $3,975. What were her sales for the month of May?

Kim sold over $20,000 in May. She received a 5% commission on the ?rst $20,000 of sales. To ?nd 5%, multiply by the decimal equivalent of 5% (0.05); $20,000 × 0.05 = $1,000. Since her total commission was $3,975, $3,975 - $1,000 = $2,975 is the amount of commission she earned on her sales over $20,000. $2,975 is 8.5% of her sales over $20,000. To ?nd the amount of her sales over $20,000, use a proportion; part/whole = %/100. Part is $2,975, and whole is what we are looking for, so let's call it x. The % is 8.5; 2975/x = 8.5/100. To solve for x, cross multiply; (2,975)(100) = 8.5x. Divide both sides by 8.5 to solve; 297500/8.5 =8.5x/8.5; x = $35,000. Her sales over $20,000 were $35,000. Her total sales were $55,000 ($20,000 + $35,000).