let

x = the number of rs.1 coins

y = the number of rs.2 coins

a money box contains rs.1 and rs.2 coins in the ratio of 5:6

x : y = 5 : 6

6x = 5y

the total value of coins in the box is rs.85

1*x + 2*y = 85

by solving the system of equations

6x = 5y

1*x + 2*y = 85

we find

x = 25 coins

y = 30 coins

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the number of 1 rupee coins is 25.