A and B together have a sum of Rs. 1680. Half of the total amount is equal to the $frac{7}{10}$ th part of total amount with B. Find the total sum with B.

Amount with B = Rs. x

$herefore frac{7 x}{10}=frac{1680}{2}=840$

$Rightarrow 7 x=840 imes 10$

$Rightarrow x=frac{840 imes 10}{7}=$ Rs. 1200