Round each weight to the nearest whole gram. Then estimate the total weight of the coins in Allen’s hand. 2.500,5.000,2.268,5.670,11.340

So the rounded weights would be 3, 5, 2, 6, and 11, as when you round, you look at the number to the right of the one you want to round to. If it's 5 or larger, you add one to the spot you're rounding to, and make the rest of the numbers after into zeroes. If it's below 5, just change the ones after the one you want to round to into zeroes and don't add one.

Then for the estimating of the weight, you would add them together. 3+5+2+6+11. That would equal 27, so the estimate weight is 27 grams.