options: Identify arithmetic patterns (including patterns in the addition table or multiplication table), and explain them using properties of operations. For example, observe that 4 times a number is always even, and explain why 4 times a number can be decomposed into two equal addends.

Solve two-step word problems using the four operations. Represent these problems using equations with a letter standing for the unknown quantity. Assess the reasonableness of answers using mental computation and estimation strategies including rounding. (This standard is limited to problems posed with whole numbers and having whole number answers; students should know how to perform operations in the conventional order when there are no parentheses to specify a particular order (Order of Operations).)
problem_activity: Rishi is trying to find the total number of clouds in the following array.
[IMG]
Rishi says "I know 3 × 9 = 27, so I can use that to help me solve."
a.   Mark the array above to show how Rishi is thinking about it.
b.   Use the fact that
$$3\times9=27$$
to find the total number of clouds in the array.


correct_option_index: 0