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
Answer: Sally took 9 sweets and Sammy 3