This is the concept of simultaneous equations:
Let the time taken to do one sum be x and time taken to do one product be y.
Total time taken to do 5 sums and seven products will be:
5x+7y=43
Total time taken to do 4 sums and 6 products will be:
4x+6y=36
This gives us the simultaneous equations:
5x+7y=43
4x+6y=36
multiply the top equation by 4 and the bottom equation by 5 then subtract the bottom equation from the top gives us:
-2y=-8
thus:
y=4
next
multiply the top equation by 6 and the bottom equation by 7 then subtract the bottom from the top equation gives us:
-2x=-6
hence;
x=3
therefore:
Total time taken to do 1 sum is x=3 nanoseconds
Total time taken to do 1 product is y=4 nanoseconds
