Grade 7 formula

[Guest]

This is probably grade 7 math but I am stumped at the proper equation Thanks

If it costs .06 per 1000 and .12 per 500. What is the cost per 800? I need the formula please to figure out from 100-1000.

[Guest]

1000 - 500 = 500
800 is 300 more than 500
assume linear cost relationship
cost of 800 is cost of 500 minus 3/5 of the cost difference from 1000 to 500

0.12 - (3/5 x 0.06) = 0.12 - 0.036 = 0.84

......Simple.............

[Guest]

Sorry... error in last post......should read as.....

0.12 - 0.036 = 0.084


....Simple to make mistakes......