Answer:
18
Explanation:
The trick here is to answer the question without a calculator otherwise it is a no-brainer
Couple of ways to reason and solve this. This is my approach
- It takes 17 cups to make 1 smoothie
- To make 2 smoothies you would need 17 x 2 = 34 cups
- To make 20 smoothies you would need 34 x 10 = 340 cups
- Since 306 is less than 340 we know the answer is less than 20 so it is either 18 or 19 smoothies
- If you make 19 smoothies (1 less than 20) then you would need 17 less cups so that would mean 340 - 17 = 323; 306 is still less than 323 so the answer is not 19 which leaves 18 as the right answer.
Another way....
17 x 18 will result in a digit ending in 6(7 x 8 =56) whereas 17 x 19 will result in a digit ending in 3(7 x 9 = 63) so the correct answer is 18
I hope that was not too confusing :)