Mental Strategies

{"questions":[{"content":"Calculate 36 + 19 mentally.<br>[[input-1]]","widgets":{"input-1":{"type":"input","answer":"55"}},"hints":["Add 20, then subtract 1."],"explanation":"36 + 20 - 1 = 55."},{"content":"Calculate 72 − 29 mentally.<br>[[input-2]]","widgets":{"input-2":{"type":"input","answer":"43"}},"hints":["Subtract 30, then add 1."],"explanation":"72 − 30 + 1 = 43."},{"content":"Calculate 48 + 25 mentally.<br>[[input-3]]","widgets":{"input-3":{"type":"input","answer":"73"}},"hints":["Make 50 by moving 2."],"explanation":"50 + 23 = 73."},{"content":"Calculate 100 − 46 mentally.<br>[[input-4]]","widgets":{"input-4":{"type":"input","answer":"54"}},"hints":["Subtract 40, then 6."],"explanation":"100 − 40 − 6 = 54."}],"mix":1}