What numbers are 3428 and 432 fairly close to? Once you come up with those, then you should be able to add in your head and estimate the answer.
3428 -- fairly close to 3400
432 -- fairly close to 450
When you add those two in your mind, you should get 3850.
Use compatible numbers to complete this problem. Then estimate the sum.
3,428
+432
_____
2 answers
3860