Don recently received his first credit card, a mastercard with a credit line of $500. in the first month he had it, he ran up charges of $475. how much of that must he pay if he wants to charge an airline ticket which costs $200 on his card without going over his credit limit?

He has to pay at least $175.

Explanation:

As he wants to charge $200 airline ticket cost to his credit card without exceeding the credit line of $500, his available limit at the time the airline ticket is charged should be $200 or above; or the outstanding charge should be $300 or below ( that is, $500 - $200).

As his outstanding charge is $475, he needs to pay at least $175 ( that is, $475 - $300) in order to bring his available limit from $25 ( that is $500 - $475) to at least $200 so that the airline ticket cost can be charge to his credit card without going beyond the given limit of $500.

No, the triangular numbers are not a direct variation. There is not a constant of variation between a number and its position in the sequence. The ratios of the numbers to their positions are not equal. Also, the points (1, 1), (2, 3), (3, 6), and so on, do not lie on a line.

Hope this helps!!! :)