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 answers:
A) 120 B) 125 C) 110 D) 115 E) 121
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= 
<gadget id="calculator">4*30</gadget>
<output>120</output>
120   The machine would be 120 pencils in 1 hr 30 min.   120nswer: 120
<result>A</result>
A machine, working at a constant rate, manufactures 40 pencils in 30 minutes. How many pencils does it make in 1 hr 30 min?