Q.Which is better investment? 20% stock at $\text{\text{₹}}\,140$ (or) 10% stock at $\text{\text{₹}}\,70$.

Both stocks return the same $\tfrac{100}{7}\%\approx14.29\%$ per rupee invested, so neither is the better buy.

Method — compare percentage yield (income per ₹100 invested). For a $c\%$ stock bought at market price $M$, income on ₹100 face value is ₹$c$ for a cost of ₹$M$, so

$\text{yield}=\frac{c}{M}\times100.$

$20\%$ stock at ₹140: $\ \dfrac{20}{140}\times100=\dfrac{100}{7}=14.29\%.$

$10\%$ stock at ₹70: $\ \dfrac{10}{70}\times100=\dfrac{100}{7}=14.29\%.$

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