christoph wrote:

When which of the seven digits in 452*36*17 is plus 1, the product will increase by less than 1000?

A. 1

B. 2

C. 5

D. 7

E. 4

Sorry, I would explain it more clearly:

452*36*17 = 904*18*17

If adding 1 to 18 : the product will increase by 904*17 >> 1000 ( much much larger than 1000)

similar to adding 1 to 17

As we see, even we add 1 to the unit digits of 36 or 17, the product increases a lot more than 1000 ---> not to mention adding 1 to the tens digit of 38 or 17

Adding 1 to 2 of 452 , the product increases by 36*17 ( this product < 720 <1000) ---> satisfies

That's why B it is.