I have earlier presented the SUMPRODUCT function.

When PRODUCT is simply same as multiplying cell, SUMPRODUCT is sum of PRODUCTS.

This picture illustrates PRODUCT and SUMPRODUCT functions.

PRODUCT(B3:D3) is same as B3*C3*D3.

PRODUCT(B3:D3)+ PRODUCT(B3:D3) is same as SUMPRODUCT(B3:B4;C3:C4;D3:D4)

A person has a salary of 3000. In the middle of the month the person receives a raise of 240 €.

 In a month there are 22 working days. The persons salary is 3000 during 15 workdays of the month and 3240 for seven working days.

15/22 days the salary is 3000 and 7/22 days 3240. The salary during that month is 3076,36.

That can be calculated with SUMPRODUCT(B4:B5;C4:C5) which might be easier than traditional way in C7.