A machine, working at a constant rate, manufactures 40 pencils in 30 minutes. How many pencils does it make in 1 hr 30 min?	Choose the correct choice from the following options: A) 120 B) 125 C) 110 D) 115 E) 121

Rationale: "change 1 hr 30 min to 90 min . for this , we need to set up a simple proportion of pensils per time 40 / 30 = s / 90 the absolutely worst thing you could do at this point in the problem is to cross - multiply . that would be a supremely unstrategic move . instead , cancel before you multiply . for what we can and can ’ t cancel in a proportion , seethis post . we can cancel the factor of 10 in the 40 and 30 . 4 / 3 = s / 90 we can cancel the common factor of 3 in the two denominators . 4 / 1 = s / 30 . now that the fraction is entirely simplified , we can cross - multiply . s = 4 * 30 = 120 the machine would be 120 pencils in 1 hr 30 min . answer : a"
Answer: A