Let the no. of 10 paise coins be x and the no. of 50 paise coins be y,
According to question, total no. of coins = 70
or, x + y = 70
or, x = 70-y ............ (i)
Now total value of money is Rs. 19 (1900 paise)
or, 10x + 50y = 1900
or, 10(70-y) + 50y = 1900 [Putting the value of x from eqn (i)]
or, 700 - 10y + 50y = 1900
or, 40y = 1200
or, y = 30
Therefore, there are 30 fifty paisa coins.
And, x = 70-y
or, x = 70-30 = 40
Hence, there are 40 ten paisa coins.
Hope that helps !!