a . 2 * 125 * 2002 * 8 * 5
= 2 * 5 * 125 * 8 * 2002
= 10 * 1000 * 2002
= 20020000
c. 28 * 47 + 28 * 43 + 72 * 29 + 72 * 61
= 28 * ( 47 + 43 ) + 72 ( 29 + 61 )
= 28 * 90 + 72 * 90
= 90 ( 28 + 72 )
= 90 * 100
= 9000
d . 26 * 54 + 52 * 73
= 26 * 54 + 26 * 146
= 26 ( 54 + 146 )
= 26 * 200
= 5200