A machine, working at a constant rate...

swerve wrote:A machine, working at a constant rate, manufactures 36 straplers in 28 minutes. How many straplers does it make in 1 hr 45 min?

A. 125
B. 128
C. 135
D. 144
E. 150

We can solve this using equivalent ratios

We're comparing machine output (measured in # of staplers) with time (in minutes)

1 hr 45 min = 105 minutes
Let x = # of staplers that can be made in 105 minutes

We get: 36/28 = x/105
Cross multiply to get: (28)(x) = (36)(105)
Divide both sides by 28 to get: x = (36)(105)/(28)
To calculate this, it's useful to recognize that 105 = (7)(15) and 36 = (4)(9) and 28 = (4)(7)
So, we get: x = (4)(9)(7)(15)/(4)(7)
Simplify to get: x = (9)(15)
= 135

Answer: C

Cheers,
Brent