Thank you for using the timer!
We noticed you are actually not timing your practice. Click the START button first next time you use the timer.
There are many benefits to timing your practice, including:
answer is C. here is how i do it:
remember that for a product to be even - one multiplier must be even.
st1. if d is 1 c can be anything hence insufficient
st2. same as st1. if d is 2 c can be anything.
if c is odd, then from st1 d+1 must even. from st2 d+4 must be even (c is odd means c+2 is odd as well).
but d+1 and d+4 cannot be both even at the same time.
hence c cannot be odd. so c is even.