Mira is making telescopes, each consisting of 2 lenses, 1 tube, and 1 eyepiece. Lenses can be purchased only in packs of 50, tubes only in packs of 10, and eyepieces only in packs of 30. However, half of the lenses in each pack are not usable for telescopes. If all parts are used only for the telescopes, what is the minimum number of lenses Mira must purchase to make a set of telescopes with no leftover components other than the unusable lenses?
Choose the correct choice from the following
A) 60 B) 150 C) 1800 D) 700 E) 7,500
I'd use backsolving for this question.   Check C:   1800 lenses = 900 usable lenses = 450 tubes = 450 eyepieces. We CAN buy 450 tubes and 450 eyepieces, so that not to have leftovers.   Answer: 1800.
<result>C</result>
Mira is making telescopes, each consisting of 2 lenses, 1 tube, and 1 eyepiece. Lenses can be purchased only in packs of 50, tubes only in packs of 10, and eyepieces only in packs of 30. However, half of the lenses in each pack are not usable for telescopes. If all parts are used only for the telescopes, what is the minimum number of lenses Mira must purchase to make a set of telescopes with no leftover components other than the unusable lenses?