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Question

A frog tries to come out of a 30 m deep dried well with slippery walls. In every jump the frog jumps up by 70 cm, but slides down 30 cm. What is the minimum number of jumps required for the frog to come out of the well?

The correct answer is
75

To solve this problem, we must determine how many jumps the frog needs to make to get out of the 30-meter deep well.

  1. The frog jumps up \(70 \text{ cm}\) on each jump and then slides back down \(30 \text{ cm}\).
  2. The effective height gained after each jump is: \(70 \text{ cm} - 30 \text{ cm} = 40 \text{ cm}\)
  3. First, convert the depth of the well to centimeters: \(30 \text{ m} = 3000 \text{ cm}\)
  4. Determine how many effective jumps of \(40 \text{ cm}\) each are needed to reach just below the rim of the well: \(\frac{3000 \text{ cm}}{40 \text{ cm per jump}} = 75 \text{ jumps}\)However, with 75 full jumps, let's consider the scenario:
  5. After 74 jumps, the frog would have climbed: \(74 \times 40 \text{ cm} = 2960 \text{ cm}\)
  6. This means at the start of the 75th jump, the frog is 2960 cm up, requiring one more \(70 \text{ cm}\) jump to finish the climb without slipping back again.

Therefore, the minimum number of jumps required for the frog to completely get out of the well is 75.

Summary: The frog effectively gains \(40 \text{ cm}\) per jump, and after 74 jumps, it is at 2960 cm. The 75th jump allows it to reach the top.

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  5. In a group of 120 persons, 80 are Indians and rest are foreigners. Further, 70 persons in the group can speak English, The number of Indians who can speak English is

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