Tickets for a concert cost $2 each for children and $5 each for adults. A group of 30 people consisting of children and adults paid a total of $87 for the concert. How many adults were in the group?

Let,

the no. of adults be "x"

then, the no. of childern = total people - total adults

= (30 - x)

Now,

According to the quesiton,

2 (30 - x) + 5x = 87

60 - 2x + 5x = 87

60 + 3x = 87

3x = 87 - 60

3x = 27

x = 27 / 3

x = 9

So, there were 9 adults in the group