Question: What's 40 years old and just as sweet and icy as the day as it was born?

Answer: A Slurpee (search)!

The famed hot-weather treat celebrated the big 4-0 on Monday.

Hard to believe it was four decades ago that 7-Eleven began testing three specially designed ice machines in the Midwest — and immediately had a smash hit on its hands.

"This is the quintessential summer treat," raved Tom Ruprecht, 31, a writer for David Letterman (search), as he eagerly sucked down a Slurpee at the new 7-Eleven in Manhattan.

Slurpees may still taste the same, but one thing has changed forever: the price. Forty years ago, they cost about 10 cents. Now they're $1.19 to $1.65.

For the record, the idea for Slurpee originated in 1959 in Kansas when Omar Knedlik's (search) soda machine at his drive-in burger joint busted — and he started serving half-frozen bottled soda from his freezer. Customers went wild.

Knedlik hired a Dallas company to create a machine that could make the slushy glop, but the equipment failed to make a splash until 1965, when 7-Eleven became interested and bought three of the machines.

An ad agency dreamed up the name "Slurpee" after noting the sound the concoction makes while getting sucked through a straw.