Question

Use mental math to estimate the unknown number 4210 divided by 6

Answer 1

6 times 7 42 plus 4210

Answer 2

6 divides into 42 producing a quotient of 7 and no remainder.  All that's left is to divide 6 into 10.  That produces 1 with a remainder of 4.

So you could say immediately that 4210 divided by 6 is approx. 71.