Option (b) is correct.

Amount in 5 years = 5200

Amount in 7 years = 5680

Which means interest for two years

= 480 (Since it is simple interest)

So, Interest per year = 480/2 = 240

Intrest for 5 years = 240 x 5 = 1200

So, Principal = Amount – Interest

= 5200 – 1200

= 4000

Hence rate% = 1200 = (4000x r x5)/100 = r => 6%

विकल्प (b) सही है।

5 वर्षों में राशि = 5200

7 वर्षों में राशि = 5680

जिसका मतलब है दो साल के लिए ब्याज

= 480 (चूंकि यह साधारण ब्याज है)

तो, प्रति वर्ष ब्याज = 480/2 = 240

5 वर्षों के लिए अंतराल = 240 × 5 = 1200

तो, मूलधन = राशि – ब्याज

= 5200 – 1200

= 4000

अतः, दर% = 1200 = (4000× r ×5)/100

r ⇒ 6%