Abdul's seventh grade class is going on a field trip to a history museum. There are x students and y teachers going on the trip. Tickets for students are $10 each and tickets for teachers are $20 each. The history museum gave the class 20% off as part of a group promotion.
The cost of tickets for the students is $10 * x.
The cost of tickets for the teachers is $20 * y.
The total cost of tickets before the discount is $10x + $20y.
The total discount is 20% of ($10x + $20y), which is (20/100) * ($10x + $20y) = $2x + $4y.
The total cost of tickets after the discount is $10x + $20y - ($2x + $4y).
Simplifying the expression, we get $10x + $20y - $2x - $4y = $8x + $16y.
Therefore, the final cost of tickets for the field trip is $8x + $16y.