tiq wrote...
....
I need a formula on sheet 1 column I that finds the corresponding number on
Sheet 2 and adds up the numbers in column D.

sheet 1 Column c row 1 has 40
Sheet 1 Column c row 20 has 15

Sheet 2 Column a row 1 has 40 and column D has 10
Sheet 2 Column a row 2 has 15 and column D has 3
Sheet 2 Column a row 3 has 40 and Column D has 5

On sheet 1 Column I row 1 should read 15
On sheet 1 Column I row 20 should read 3

Sheet1!I1:
=SUMIF(Sheet2!$A$1:$A$1000,C1,Sheet2!$D$1:$D$1000)

Fill Sheet1!I1 down as far as needed.