Hey Jessica,

Kindly refer to the worked solution below:

Total value of all the coins at first = $20

At first, value of 40 more 20cent coins = $8

Same unit (qty) of both 20cent and $1 coins = $20 - $8 = $12

using Number x Value method, we have ...

( 1u x 20 ) + ( 1u x 100 ) --> 1200 ( converting money to cents , and 1u -> same number/qty of both types of coins )

20u + 100u --> 1200

120u --> 1200

1u --> 1200 / 120 = 10

So the value of the $1 coins = 1u x $1 = 10 x $1 = $10

Since total value of both types of coins is $20, the value of all the 20cent coins = $20 - $10 = $10

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Trust the above helps.

Any clarification , pls do not hesitate to ask.

Cheers,

Edward