Mary has 21 coins whose total value is 72 shillings. There are twice as many 5 shilling coins as there are 10 shilling coins, the rest are 1 shilling coins. Find the number of 10 shilling coins that Mary has
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let the no. of 10 shilling coins = x
no. of 5 shilling coins =2x
let the no. of 1 shilling coins = y
no. of coins = x+2x+y =21
=3x+y=21
y= 21- 3x
total value is 72
=10x+(2*5x)+y =72
=20x +y =72
substitute y in above equation
20x+21-3x =72
17x = 51
x= 3
no. of 10 shillings = 3
no. of 5 shillings = 6
no. of 1 shilling = 12
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