Bunuel
Of the 24 students in a typing class, 9 can type a basic business letter in an average of \(5 \ \frac{1}{2}\) minutes, while the other 15 students can type the same letter in an average of \(7 \ \frac{1}{5}\) minutes. What is the average amount of time it takes, in minutes, for a student in the typing class to type a basic business letter?
A 6 1/8
B 6 11/80
C 6 7/20
D 6 1/2
E 6 9/16
Let us convert the fraction in decimals, as decimals will be more friendly here.\(5 \ \ \frac{1}{2}=5.5\) and \(7 \ \ \frac{1}{5}=7.2\)
ApproximationIf both were of equal quantity, the overall average would be \(\frac{7.2+5.5}{2}=6.35\)
As the options are in ascending order, only D and E are left.
D is 6.5, which is very close to 6.35, but 9 and 15 are pretty far off
E is the answer.
Weighted average method.............9........avg.........15
............5.5.......x...........7.2
Thus, \(\frac{7.2-x}{x-5.5}=\frac{9}{15}\)
\(\frac{7.2-x}{x-5.5}=\frac{3}{5}\)
\(36-5x=3x-16.5\)
\(8x=36+16.6=52.5...........16x=52.5*2=105..........x=\frac{105}{16}=6 \ \frac{9}{16}\)
AlgebraTotal time for all 24 = \(9*5.5+15*7.2=49.5+108=157.5\)
Average = \(\frac{157.5}{24}=\frac{315}{48}=\frac{105}{16}\)
E