Discussion
Raju has 14 currency notes in his pocket consisting of only Rs. 20 notes and Rs. 10 notes. The total money value of the notes is Rs. 230. The number of Rs. 10 notes that Raju has is
Answer: A
Raju has 5 notes of Rs. 10.
Let t be the number of Rs. 10 notes and w the number of Rs. 20 notes:
\[ \begin{aligned} t + w &= 14 \\ 10t + 20w &= 230 \\ 10t + 20(14 - t) &= 230 \\ 280 - 10t &= 230 \Rightarrow t = 5 \end{aligned} \]
So he has 5 notes of Rs. 10 and 9 of Rs. 20: 50 + 180 = 230. The option 9 is the number of Rs. 20 notes, the usual slip of solving for the wrong variable. 6 and 10 give totals of 220 and 180.
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