A change making machine contains 1 rupee, 2 rupee and 5 rupee coins. The total number of coins is 300. The amount is Rs. 960. If the number of 1 rupee coins and the number of 2 rupee coins are interchanged, the value comes down by Rs. 40. The total number of 5 rupee coins is
Answer: B
Let the number of Re. 1, Re. 2 and Re. 5 coins be x, y and z respectively.
x + y + z = 300 ...(i)
x + 2y + 5z = 960 ...(ii)
2x + y + 5z = 920 ...(iii)
Adding equation (ii) and equation (iii), we get,
3x + 3y + 10z = 1880 ...(iv)
Multiply equation (i) by 3, we get,
3x + 3y + 3z = 900 ...(v)
Subtracting equation (v) from equation (iv), we get,
7z = 980
∴ z = 140
Hence, option (b).