She can use 68 + 20 = 88 to help by noticing that the 20 is ahead of 19 by 1. She can easily mentally turn the 20 into a 19 and realized that the 88 would become 87.
Answer:
90 arrangements
Step-by-step explanation:
Since there are no repititions of letters, there are unique 10 letters in total.
THe number of arrangements would be 2 permutation 10. We need the formula for permutation. That is:

Now, n = 10 [total] and r is 2, so we have:

So, there can be 90 arrangements
Okay what you need I’ll help you with whatever
Answer:
5.66 inches
Step-by-step explanation:

a² + 7² = 9²
a² + 49 = 81
a² + 49 - 49 = 81 - 49
a² = 32
a = square root of 32
a = 5.6568 or 5.66 inches
I used the Pythagorean Theorem to solve this.