What sum of money will amount to 520 Rs. in 5 years and to 568 Rs. in 7 years at simple interest?

What sum of money will amount to 520 Rs. in 5 years and to 568 Rs. in 7 years at simple interest?
[A]220 Rs.
[B]400 Rs.
[C]120 Rs.
[D]510 Rs.

400 Rs.
Simple interest for 2 years = (568 – 520) Rs. = 48 Rs.
∴ Interest for 5 years =
= \frac{48}{2}\times 5 = 120 Rs.
Principal = (520 – 120) = 400 Rs.
Hence option [B] is the right answer.

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