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An app earns (500) rupees on the first day and the income increases by (100) rupees each next day. What is the total income in (10) days?

Answer and explanation

Correct answer: (9500)

The direct answer is C: ₹9,500. The daily incomes form an arithmetic progression because the first income is ₹500 and the same amount, ₹100, is added each day. Thus, the first term is \\(a=500\\), the common difference is \\(d=100\\), and the number of terms is \\(n=10\\). The tenth-day income is \\(a_{10}=a+(n-1)d=500+9(100)=1400\\). The total can be found by \\(S_n=\\frac{n}{2}[2a+(n-1)d]\\): \\(S_{10}=\\frac{10}{2}[2(500)+9(100)]=5(1900)=9500\\). Option A, ₹9,000, is wrong because it does not add the ten correct terms. Option B, ₹9,250, is wrong because the arithmetic calculation is incomplete or inaccurate. Option C, ₹9,500, is correct. Option D, ₹9,750, is also too high and does not follow the given first term and increase. A quick check is to list the terms: 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300 and 1400; their sum is ₹9,500. Memory cue: identify first term, common difference and number of terms before using the AP sum formula.

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