Maya has 2x as many white beads as black beads. After using 40 white and 5 black to make a necklace she has 3x as many black beads as white. How many black beads she started with?
Step 1
Suppose Maya has B black beads and so has 2B white beads.
She used 5 black beads and 40 white beads,
so she was left with black beads and white beads.
Now as she has 3 times as many black beads as white,
or
or
or i.e.
Hence, she started with 23 black beads.