4 boys and 3 girls spent 120 Rs. on the average, of which boys spent 150 Rs. on the average. Then what would be the average amount spent by the girls is :

4 boys and 3 girls spent 120 Rs. on the average, of which boys spent 150 Rs. on the average. Then what would be the average amount spent by the girls is :
[A]60 Rs.
[B]80 Rs.
[C]90 Rs.
[D]100 Rs.

80 Rs.
Total expenditure = 120 \times 7 = 840\ Rs.
Total expenditure of 4 boys = 150 \times 4 = 600\ Rs.
Total expenditure of 3 girls = 840 - 600 = 240\ Rs.
∴ Their average expenditure = \frac{240}{3} = 80\ Rs.
Hence option [B] is correct answer.

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