How many cubes on needed to build the ninth figure?
1st: 4 cubes
2nd: 7 cubes
3rd:10 cubes
A) 26 cubes
B) 27 cubes
C) 28 cubes
D)29 cubes
B) 27 cubes
To find the number of cubes needed for the ninth figure, we can see that each new figure is adding 3 more cubes than the previous figure.
4 + 3 = 7
7 + 3 = 10
10 + 3 = 13
13 + 3 = 16
16 + 3 = 19
19 + 3 = 22
22 + 3 = 25
25 + 3 = 28
28 + 3 = 31
So, the ninth figure would need 31 cubes, but since we're asked for the number of cubes needed for the ninth figure, we stop the sequence at the eighth figure which is 25 cubes.
Adding all the cubes:
4 + 7 + 10 + 13 + 16 + 19 + 22 + 25 = 116
Therefore, the ninth figure would need 27 cubes.