Final answer:
The sum of 6.75 and 3.25 using mental math is 10.
Step-by-step explanation:
To find the sum using mental math for the numbers 6.75 and 3.25, you can simply recognize that 0.75 and 0.25 make a whole number. Adding 6 (from 6.75) to 3 (from 3.25), you get 9. To this, you add the whole number obtained from 0.75 + 0.25, which is 1, giving you a sum of 10. Therefore, 6.75 + 3.25 equals 10.