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Problems Involving Adding and Subtracting within 1000

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Problems Involving Adding and Subtracting within 1000: Very Difficult Problems with Solutions

By Catalin David

Problem 1

625 - [625 - (247 + 156)] =

Solution:
625 - [625 - (247 + 156)] = 625 - (625 - 403) = 625 - 222 = 403

Problem 2

125 + 135 + 145 + 155 + 165 + 175 =

Solution:
We notice that the difference between the terms is the same. We can calculate more easily by adding the terms like this.
(125 + 175) + (135 + 165) + (145 + 155) = 300 + 300 + 300 = 900

Problem 3

Calculate
213 + 321 + 462 + 543 - 212 - 320 - 461 - 542 =

Solution:
We can calculate easier this way:
213 + 321 + 462 + 543 - 212 - 320 - 461 - 542 = (213 - 212) + (321 - 320) + (463 - 461) + (543 - 542) = 1 + 1 + 1 + 1 = 4

Problem 4

Tim has \$683. If he gives Matt \$324, then they will both have the same amount of money. How much money did Matt have before?

Solution:
Tim will have \$683 - 324 = 359, so Matt will have \$359 too. Before receiving the money, Matt had \$359 - \$324 = \$35

Problem 5

90 toys were sold in the first day at a shop. In each of the following three days, 74 more toys were sold than the day before. What's the number of toys sold in the 4 days?

Solution:
The second day, 90 + 74 = 164 toys were sold.

The third day, 164 + 74 = 238 toys were sold.

The fourth day, 238 + 74 = 312 toys were sold.

The total number of toys sold is
90 + 164 + 238 + 312 = 804

Problem 6

Can we build a triangle whose sides are 185 cm, 378 cm and 563 cm?

Solution:
We observe that 185 + 378 = 563
In this case, the points should be on the same line, so we can't build a triangle.

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