A hotel charges $90 per day for a double room $80 per day for a single room. If a total of 80 single and double rooms are occupied and a total revenue of $6930 is taken in, how many of each type of room are there?

the number of single room is 27 and the number of double room  is 53

Step-by-step explanation:

Let x is the number of single room

Let y is the number of double room

We know that:

x + y = 80 <=> x = 80 -y (1)

80x +90y= 6930 (2)

Substitute (1) in (2) we have:

80 (80 - y) + 90y = 6930

<=> 6400 - 80y +90y = 6930

<=> y = 53

> x = 80 - 53 = 27

the number of single room is 27 and the number of double room  is 53

because linear equations are a lot simpler than quadratics equations, and linear equations formula is a lot easier to memorize. that's why i think they're harder.

ok then what happened.