MENTAL ARITHMETIC: SUBTRACTION PROBLEMS 3 Completing 100 19. If an item costs 59¢, and you give a dollar bill, how much is your 20. What number must you add to each of these to make 100?
21. How much must you add to each of these to make $10.00?
22. 44% voted No. What percent voted Yes? 56% 23. The price of a jacket was reduced by 35%. What percent of the 24. Use the complement to 100 of the smaller number to calculate 109 − 75 25 + 9 = 34 103 − 85 = 18 132 − 78 = 54 115 − 92 = 23 106 − 47 = 59 124 − 88 = 36 111 − 35 = 76 130 − 79 = 51 124 − 75 = 49 115 − 86 = 29 152 − 94 = 58 25. William Shakespeare was born in 1564 and died in 1616. How old 26. How long ago was the Stock Market crash of 1929? Start at 1929, and count to the present year. 27. How many years have passed since the discovery of America Start at 1492, and count to the present year. 28. How long ago did the Pilgrims land at Plymouth Rock (1620)? Start at 1620, and count to the present year. 29. How many years have passed since the signing of the Declaration of Start at 1776, and count to the present year. 30. How long ago was the Battle of Hastings (1066)? Start at 1066, and count to the present year. Rounding off 31. Consider 231 − 95. 31. a) If you add 5 to both numbers, how will the difference change ?
The difference will 31. b) Calculate the difference mentally by rounding off. 236 − 100 = 136 32. How does compensating in subtraction differ from compensating in
In subtraction, if we add to one number, we must add it to the other number. But in addition, if we add to one number, we must 33. Calculate each column mentally by rounding off the smaller number.
34. The cents in the smaller number are less. Calculate mentally by
35. The cents in the smaller number are more. Calculate mentally
9.20 − 3.72 = 5.48 7.12 − 2.49 = 4.63 8.23 − 6.84 = 1.39 9.12 − 4.25 = 4.87 5.21 − 3.75 = 1.46 Continue on to the next Lesson. or Return to the previous section. Please make a donation to keep TheMathPage online. Copyright © 2015 Lawrence Spector Questions or comments? E-mail: themathpage@nyc.rr.com |