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If a, b, c, d are in proportion (a : b :: c : d), then by componendo and dividendo, (a + b)/(a - b) equals
A(c - d)/(c + d)
B(a + d)/(b + c)
C(a - d)/(b + c)
D(c + d)/(c - d)
Answer & Solution
Correct answer: D. (c + d)/(c - d)
1. Given a/b = c/d (proportion form).
2. Componendo: (a + b)/b = (c + d)/d.
3. Dividendo: (a - b)/b = (c - d)/d.
4. Dividing the two: (a + b)/(a - b) = (c + d)/(c - d).
_Source: ICAI BoS Foundation Paper 3, Ch 1 Unit II 'Proportions', p.10_
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