Estimate first
Helps you catch place-value slips: round, estimate, then check that the exact answer is close.
Step 1Round each number to its first digit: 80 stays 80; 4 stays 4.
Step 2Estimate: 80 × 4 = 320.
Step 3Now work it out exactly: 80 × 4 = 320.
Step 4Compare: the exact answer matches the estimate of 320.