Question

The ratio of adults to children attending a new exhibit at the museum was found to be 8:5. Based on this ratio, if 390 people attended one day, how many would be children?

Answer 1

$8x+5x=390\\ 13x=390\\ x=30\\\\ 5x=5\cdot30=\boxed{150}$

Answer 2

The fastest method would be to add 8+5 and then divide 390 by it. And then that would be your base unit which you multiply to 8 and 5 to get your answers

8+5=13
390/13
30
30x8=240 adults
30x5=150 children