LCM means Least Common Multiple. To find this, we start listing the multiples of #5# and #8# until we find one that matches both
#color(white)(. . . .) 5 color(white)(. . . . . . . . . . . . . . . . . . . .) 8#
#. . . . . . . . . .# #color(white)(0 0 0 0 0 0 0 0 0 )# #. . . . . . . . . . .#
#1 xx 5 = 5# #color(white)(. . . . . . . . . . 1)# #1 xx 8 = 8#
#2 xx 5 = 10# #color(white)(. . . . . . . . . .)# #2 xx 8 = 16#
#3 xx 5 = 15# #color(white)(. . . . . . . . . .)# #3 xx 8 = 24#
#4 xx 5 = 20# #color(white)(. . . . . . . . . .)# #4 xx 8 = 32#
#5 xx 5 = 25# #color(white)(. . . . . . . . . .)# #color(red)(5 xx 8 = 40#
#6 xx 5 = 30#
#7 xx 5 = 35#
#color(red)(8 xx 5 = 40)#
Looks like #color(red)(40# is the LCM of #8# and #5#
