Latihan tambahan

读写数复习 = ulang kaji baca dan tulis nombor 五位数的读法：先读前两位，后面加 ribu；再读后三位。后三位里哪一位是 0，那一位就不读，例如百位是 0 就不说 ratus。 例子：40 083 = empat puluh ribu lapan puluh tiga。 注意：写成文字后，再把它写回数字检查，看是不是原来的数。

review reading and writing numbers = ulang kaji baca dan tulis nombor To read a five-digit number, read the first two digits and add ribu, then read the last three digits. A 0 in the last three digits is not read; for example, when the hundreds digit is 0, do not say ratus. Example: 40 083 = empat puluh ribu lapan puluh tiga. Watch out: after writing the words, change them back into numerals to check you get the same number.

乘法复习 = ulang kaji darab 用竖式：先用 25 的个位 5 去乘，再用十位（代表 20）去乘，第二行个位先写 0，最后两行相加。乘 25 还有一个巧法：4 个 25 是 100，可以先看被乘数里有几个 4。 例子：64 × 25 → 64 = 16 × 4，16 × 100 = 1 600。 注意：第二行漏了 0，得数会小很多。

review multiplication = ulang kaji darab With the column method, multiply by the ones digit 5, then by the tens digit (which stands for 20) with a 0 at the start of the second row, and add the rows. There is also a shortcut for × 25: four 25s make 100, so see how many 4s are in the other number. Example: 64 × 25: 64 = 16 × 4, so 16 × 100 = 1 600. Watch out: a missing 0 in the second row makes the result far too small.

减法复习 = ulang kaji tolak 被减数有很多个 0 时，连续借位容易出错。可以把两个数都减去 1：被减数变成一串 9，这样每一位都够减，不用借位，差不变。 例子：30 000 − 4 125 = 29 999 − 4 124 = 25 875。 注意：两个数都要减 1，只减一个，差就会变。

review subtraction = ulang kaji tolak When the first number has many zeros, regrouping again and again is easy to get wrong. Take 1 from both numbers: the first number becomes a row of 9s, every column can be subtracted without regrouping, and the difference stays the same. Example: 30 000 − 4 125 = 29 999 − 4 124 = 25 875. Watch out: take 1 from both numbers; taking it from only one changes the difference.