The quantity that must be added to each term of a : b, so as to make it c : d, is
Correct Answer: ad - bc/c - d
Explanation:
Let the quantity be k.
Then, (a + k) / (b + k) = c/d
⇒ (a + k)d = (b + k)c
⇒ ad + dk = bc + ck
⇒ ad - bc = ck - dk
⇒ ad - bc = k(c - d)
∴ k = (ad - bc) / (c - d)
