Doppler effect: how frequency and wavelength change when source and observer approach

This type of question, asked 2 times: 19 Apr 2025 S1, 22 Apr 2025 S2. All 2 questions below, oldest first.

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Question 1
19 Apr 2025 S1
15 $When source of sound moves towards a stationary observer, the apparent frequency heard by him$
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Question 2
22 Apr 2025 S2
33 $When source of sound and observer both are moving towards each other, the observer will hear$
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