Perform the calculation mentally
1. 90 + 247 + 253 + 110
2. 799 - 117
3. 25 × 25 × 8
Never Mind My Bad :)
Think of ways to do them "in your head" without a pencil or calculator.
In #1, note that 90+110 = 200 and 243+257 = 500. Add 200 and 500.
#2 can be answered "on sight". No "carrying" is necessary.
#3. Note that 8x25 = 200
Multiply that by 25. The ones and tens columns remain zero.
I "saw" #3 as
25 x 4 x 25 x 2 or 100x50
To perform the calculations mentally, you can use various techniques. Here's how you can approach each calculation:
1. 90 + 247 + 253 + 110:
- Start by adding the hundreds: 200 + 200 + 100 = 500.
- Then, add the tens: 90 + 40 + 50 + 10 = 190.
- Finally, add the ones: 7 + 3 = 10. Carry over the 1 to the tens place.
- Add the partial sums together: 500 + 190 + 10 = 700.
2. 799 - 117:
- Begin by subtracting the hundreds: 700 - 100 = 600.
- Next, subtract the tens: 90 - 10 = 80.
- Finally, subtract the ones: 9 - 7 = 2.
- Combine the partial differences together: 600 + 80 + 2 = 682.
3. 25 × 25 × 8:
- Multiply the two visible numbers: 25 × 8 = 200.
- Multiply by the second 25 (ones place): 200 × 5 = 1000.
- Multiply by the first 25 (tens place): 1000 × 2 = 2000.
- The result is 2000.