David used 1/10 of his monthly salary for groceries and 3/18 of his remaining money for his car payment. He also paid twice as much money for rent as for his car payment. If David has $1,620 left after paying for groceries, car payment, and rent, how much is his monthly salary?

Explanation

Let's denote David's monthly salary as x. He spends 1/10 of his salary on groceries, so the amount spent on groceries is x * 1/10 = x/10. After groceries, he has 9/10 of his salary left.From this remaining amount, he spends 3/18 on his car payment. The car payment is calculated as (9/10)x * 3/18 = x/20.Rent is twice the car payment, so rent is 2 * (x/20) = x/10.After all these expenses, David has $1,620 left. Therefore, the equation becomes:x/10 (groceries) + x/20 (car) + x/10 (rent) + $1,620 = x.Combining terms gives x/10 + x/20 + x/10 = x - $1,620.Finding a common denominator for the fractions, we have (2x + x + 2x)/20 = x - $1,620.This simplifies to 5x/20 = x - $1,620, or x/4 = x - $1,620.So, x - x/4 = $1,620, which simplifies to 3x/4 = $1,620. Solving for x gives x = $3,600.Thus, David's monthly salary is $3,600. The other options miscalculate the expenses or the remaining balance.