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Three measuring jars have the capabilities of 15 ml, 50 ml and 30 ml. what is the least capacity which can be perfectly measured by any of the measuring jars?

  • A.100
  • B.75
  • C.150
  • D.450

Answer: C

The least capacity is 150 ml.

A quantity that each jar can measure exactly, in whole fillings, must be a multiple of 15, 50 and 30, so the least such quantity is their least common multiple:

\[ \begin{aligned} 15 &= 3 \times 5, \quad 30 = 2 \times 3 \times 5, \quad 50 = 2 \times 5^{2} \\ \text{LCM} &= 2 \times 3 \times 5^{2} = 150 \end{aligned} \]

150 ml is 10 fillings of the 15 ml jar, 5 of the 30 ml and 3 of the 50 ml. 100 is not a multiple of 15 or 30, and 75 is not a multiple of 50 or 30. 450 is a common multiple but not the least.

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