Data Sufficiency

Economist GMAT

An Internet supplier has 4 international cables. Each cable contains 4 sub-cables, which in turn are composed of 4 intertwined copper wires. Each cable is color - coded differently - cyan, indigo, magenta, sapphire.

What was the average communication transfer rate per international cable last month?

(1) The sub-cables in the cyan and indigo cables transferred 48 Gigabytes of information last month.
(2) The sub-cables in the indigo and sapphire cables transferred 26 Gigabytes of information last month.

OA E.

AAPL wrote: An Internet supplier has 4 international cables. Each cable contains 4 sub-cables, which in turn are composed of 4 intertwined copper wires. Each cable is color - coded differently - cyan, indigo, magenta, sapphire.

What was the average communication transfer rate per international cable last month?

(1) The sub-cables in the cyan and indigo cables transferred 48 Gigabytes of information last month.
(2) The sub-cables in the indigo and sapphire cables transferred 26 Gigabytes of information last month.

The answer is (E) immediately: "nothing is known about the magenta cables"

Let´s explain the argument in a proper (more formal, less intuitive-based way):

Imagine all cyan, indigo and sapphire cables fixed, with last month transference of information all satisfying both statements given (this is possible because it is an examiner´s burden).

In that situation:

If all sub-cables in the magenta cables transfer 0 Gigabytes of information last month, we will get a certain average.
If all sub-cables in the magenta cables transfer (say) 1 Gigabytes of information last month, we will get another average.

The above follows the notations and rationale taught in the GMATH method.