Correct Answer - b
(b) `5% =(1)/(20)=(21 to "Installment")/(20 to "Principal")`
Since installment is equal hence multiply equation(i) by 21 (चुकी क़िस्त बराबर है इसलिए समीकरण (i ) को 21 से गुणा कर दे ) `rArr` Total principal = 420 +400
= 820 units
`rRrr` 820 units `to ` Rs. 15
`rArr` 441 uints `to` Rs. 15
`rArr` 441 units `to` Rs. 6615
`rArr` Each installment (प्रत्येक क़िस्त) = Rs. 6615