Firstly, we’d have to find the total price paid for erasers by subtracting the overall price from the amount she paid in pencils.
$4.25 - $1.75 = $2.50
From there, we can use the amount per eraser to find out how many erasers she bought. Since she spent $2.50 in erasers, we can multiply to find our missing number.
To find the sum of an infinite geometric series having ratios with an absolute value less than one, use the formula, S=a11−r, where a1 is the first term and r is the common ratio.