Hey there,
Your question states: If four friends can eat four cakes in four days, then how many cakes can 10 friends eat in 10 days?
10 friends = 1/4
2.5 × 10 = 25
If we do 10 ×10 = 100.
25 is 1/4 of 100.
They eat 25 cakes (per) 10 days.
Hope this helps.
~Jurgen