The greatest length of the scale that can measure exactly 30 cm, 90 cm, 1 m 20 cm and 1 m 35 cm lengths is

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WEBCSC 05/2021 Common Official Paper (Morning Shift)
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  1. 5 cm
  2. 10 cm
  3. 15 cm
  4. 30 cm

Answer (Detailed Solution Below)

Option 1 : 5 cm
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Detailed Solution

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Given:

Lengths that need to be measured exactly: 30 cm, 90 cm, 1 m 20 cm, and 1 m 35 cm.

Formula Used:

Greatest length of the scale = Highest Common Factor (HCF) of given lengths

Calculation:

Convert all lengths to cm:

30 cm

90 cm

1 m 20 cm = 120 cm

1 m 35 cm = 135 cm

Find the HCF of 30, 90, 120, and 135:

Prime Factorization:

30 = 2 × 3 × 5

90 = 2 × 32 × 5

120 = 23 × 3 × 5

135 = 33 × 5

Common factors: 3 and 5

Lowest power of common factors:

31 × 51 = 3 × 5 = 15

The greatest length of the scale that can measure exactly 30 cm, 90 cm, 120 cm, and 135 cm is 15 cm.

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