Answer:
20 X 40 = 800 (split into 2 fourths) = 40
Step-by-step explanation
20 x 40 = 800;
For 2 necklaces she can split 800 into fourths.
800 - 40 = 80. (1 fourth)
80 - 40 = 40 (2 fourths)
40 - 40 = 0 (3 fourths)
She could split 800 into 2 fourths to get a number more than 0 and less then 42.
The best estimate of rounding 42 is 40. Because 40 is closer to 42.