Answer:
Your sister
Step-by-step explanation:
To determine those with better deal we will have to do some calculations
So let's start
You bought the 3 erasers for$1.00
So we will have to determine the amount you bought 1
3 erasers=$1.0
1 eraser=x
Cross multiply
3x=1
X=1/3
X=0.33333
Your sister bought 4 erasers for $1.25
So 1 eraser=x
Cross multiply
4x=1.25
X=1.25/4
X=0.3125
So we will have to compare the two prices and we will discover that your sister gets the better deal