how to add two digit mentally easily
Answer: To add two-digit numbers mentally, use one of three simple techniques: (1) Split by Place Value (add tens together, ones together, then combine), (2) Add in Chunks (keep the first number whole, add the tens of the second, then add the units), or (3) Compensation (round one number up to the nearest multiple of 10 and subtract the extra amount).
Step-by-step solution
Step 1: Understand the Left-to-Right (Tens First) Strategy
When doing addition on paper, we usually add digits from right to left starting with the ones place. However, for mental math, adding from left to right by starting with the tens place is much faster and easier to keep in memory because it immediately gives the magnitude of the answer.
Step 2: Apply Method 1: Split Both Numbers by Place Value
To solve , first decompose each number into tens and ones: and . Next, add the tens together: . Then, add the ones together: . Finally, combine the two sums: .
Step 3: Apply Method 2: Add in Chunks (Sequential Addition)
Another effective technique is adding in chunks. Keep the first number intact and break only the second number into tens and ones. Add the tens of the second number first: . Then add the remaining ones: . This requires holding only one running total in your mind.
Step 4: Apply Method 3: Compensation (Round to the Nearest Ten)
When one number is very close to a multiple of , you can round it up and adjust. For example, needs to become . Borrow from to make it , giving . Alternatively, calculate and then subtract the extra to get .