Marcus, sally and sammy decided to share 20 sweets. marcus took 8 sweets and sally took three times as many as sammy. how many sweets did sammy receive?

Hello, 

they decided to share 20 sweets, but Marcus took 8 sweets, so:

20-8=12

We have 12 sweets left.

x= number of sweets that Sally took
y= number of sweets that Sammy took

We know that Sally took three times as many as Sammy, so:
x=3y

There are 12 sweets:

x+y=12

Replacing x:

3y+y=12
4y=12
y=3

x=3*(3)
x=9 

Sally took 9 sweets and Sammy 3