Question

plzz solve Q 26
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Answer 1

difference (d)= principal(p)(rate/100)^2

21 =8400(R/100)^2
21/8400=(R/100)^2
1/400=(R/100)^2
(1/20)^2 =(R/100)^2
therefore
1/20 = R/100
100/20= R
5=R

Rate (R)=5%