Approach 1 (Stanard):
Let's assume the number of suits to be 'S' and double rooms to be 'D'.
So from the first part, we can form the equation,
Each suit costs 115$ and each double room costs 85$
So the equation we can get,
\(115S + 85D = 10890
Or, 23S + 17D = 2178\)... (2)
By "Equation (2)" \(-\) "Equation (1) \(× 17\)" we get,
\(23S + 17D - 17D - 17S = 2178 -\) \(120 ×17\) \(= 138\)
Or, \(6S = 138 \)
Or, \(S = 23\)
The answer is A.
Approach 2: A different wayIf you observe, the prices are given in such a way that one is 100 + 15 and another one is 100 - 15.
Now we can utilize this info to our advantage to do the calculation swiftly.
Had there been 60 rooms of each type the total rent would be \(60 × (115 + 85) = 12000\)
Now there is a gap of \(12000 - 10890 = $1110\)
This is happening because we have fewer suits. And for each change of one suit to a double room, we lose out on \(115 - 85 = 30$\)
So we must have missed out on \(\frac{1110}{30}\) \(= 37\) rooms.
So the number of suits should be 60 - 37 = 23