Meera 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 Meera must purchase to make a set of telescopes with no leftover components other than the unusable lenses?
Choose one.
A) 75
B) 150
C) 300
D) 3600
E) 7,500
I'd use backsolving for this question.   Check D:   3600 lenses = 1800 usable lenses = 900 tubes = 900 eyepieces. We CAN buy 900 tubes and 900 eyepieces, so that not to have leftovers.   Answer: 3600.
<result>D</result>
Meera 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 Meera must purchase to make a set of telescopes with no leftover components other than the unusable lenses?