S2 mathematics 10point

The number has a limit which is between 9000 - 9999.
You need to find a number, when it has 2 significant figures, it should be divisible by 11.
90xx, 91xx, 92xx, 93xx, 94xx, 95xx, 96xx, 97xx, 98xx, 99xx
You can neglect the last two digit since it is rounded off to 2 significant figures.
The answer can only be 98xx / 99xx,
because when the number of xx is larger than 50, it can be rounded off to 9900 and can be divisible by 11.
You can find the number that can be divisible by 13 when it is between 9850 - 9949(can not larger than 9950 because when the process of rounding off, it will become 10000).
The number can be 9919.
9919 / 13 = 763
When it is rounded off to 3 significant figures, the number becomes 9920.
9920 / 4 = 2480 (because the last two digit is divisible by 4, hence the number can be disivible by 4)
When the number is rounded off to 2 significant figures,
9900 / 11 = 900
∴ The number can only be 9919.
When you doing this kind of homework.
You need to divide the number by 13, 11, 4 without calculating.
You can times a number randomly by 13 to get the answer nearer to 9800.
And when the last two digit is disivible by 4, the whole number is disivible by 4.