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Question

If $\sqrt{45} + \sqrt{125} = 17.88$ then what will be the value of $\sqrt{180} + \sqrt{80}$ ?

This question was previously asked in
RRB NTPC 2019 CBT 1 Question Paper (8-Mar-2021) (Shift 2)
The correct answer is
22.35

Radical Simplification: Initial Expression

First, simplify the given expression \( \sqrt{45} + \sqrt{125} \).

  • \( \sqrt{45} = \sqrt{9 \times 5} = 3\sqrt{5} \)
  • \( \sqrt{125} = \sqrt{25 \times 5} = 5\sqrt{5} \)
  • Sum: \( 3\sqrt{5} + 5\sqrt{5} = 8\sqrt{5} \).

Radical Value: \( \sqrt{5} \) Determination

We are given that \( \sqrt{45} + \sqrt{125} = 17.88 \), which simplifies to \( 8\sqrt{5} = 17.88 \).

Calculate the value of \( \sqrt{5} \):

\( \sqrt{5} = \frac{17.88}{8} = 2.235 \)

Radical Simplification: Target Expression

Now, simplify the expression whose value needs to be found: \( \sqrt{180} + \sqrt{80} \).

  • \( \sqrt{180} = \sqrt{36 \times 5} = 6\sqrt{5} \)
  • \( \sqrt{80} = \sqrt{16 \times 5} = 4\sqrt{5} \)
  • Sum: \( 6\sqrt{5} + 4\sqrt{5} = 10\sqrt{5} \).

Final Value Calculation

Substitute the calculated value of \( \sqrt{5} \) into the target expression \( 10\sqrt{5} \):

\( 10\sqrt{5} = 10 \times 2.235 \)

\( 10\sqrt{5} = 22.35 \).

Alternatively, use the given value relation directly:

Since \( 8\sqrt{5} \) corresponds to \( 17.88 \), then \( 10\sqrt{5} \) corresponds to \( \frac{10}{8} \times 17.88 \).

\( \frac{10}{8} \times 17.88 = \frac{5}{4} \times 17.88 = 5 \times 4.47 = 22.35 \).

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