Maths

3390+6859-3521
=3400-10+6800+59-3500-21(break down terms)
=3400-3500+6800-10+59-21(rearrange)
=-1000+6800-31+59(simplify some of them)
=6800-1000+59-31(rearrange again)
=6700+28
=6728
Using these steps, you can find out the answer without using the calculator.

直式計算?
3390
+ 6859
=10249

10249
- 3521
= 6728

3390+6859-3521=6728

IQ題來的?
如果唔係....答案就係6728啦..