Play for practise or challenge the world in Google Play! Add, subtract or multiply combinations of 1s, 10s, and 100s with a choice of seconds-per-answer and lives-per-game. There is also an option to get double points if you answer in half the time given. The usual scoring system is 3 points for a correct answer, and 1 point for an answer which is within 10% of the correct answer, so you don’t need the exact answer to score points. In no time you’ll be correctly estimating sums like 725 x 347, and you’ll be aided by seeing the actual answer after each question. Whatever your age, there’s a setting for you.

‘Estimate’ has space for 10 different users on one device so even the largest of families can keep track of, and try to beat, their individual scores.

Link: https://play.google.com/store/apps/details?id=com.RobertHendryGames.Estimate