a) Front-end technique (rounding off the leftmost digit of the addends)
368 ≈ 400 (3 is the leftmost digit, rounded off to 4 since the digit to its left is
more than 4))
+ 231 ≈ 200 (2 is the leftmost digit)
600 Sum
b) Estimate by rounding off to the largest place value of each addend
368 ≈ 400 (hundreds is largest place value)
+ 231 ≈ 200 (hundreds is the largest place value)
600 sum