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:
The diameter of the model is 14.4 inches.
Step-by-step explanation:
The Diameter of the moon = 2,160 miles
The scale on the model represents 1 in = 150 miles
Let the model represents k inches in 2,160 miles.
So, by the Ratio of Proportionality:

⇒
or, k = 14.4 inches
⇒On the scale 2160 miles is represented as 14.4 inches
Hence the diameter of the model is 14.4 inches.
If the diagonals of a quadrilateral bisect all the angles, then it's a rhombus, converse of a property. If the diagonals of a quadrilateral are perpendicular bisectors of each other, then it's a rhombus, converse of a property.