Multiplication by 5: Multiply by 10 (just place 0 after the original number) and divide the result by 2.

Multiplication by 6: Sometimes subsequent multiplication by 3 and then 2 is easy.
Multiplication by 9: Multiply by 10 (just place 0 after the original number) and subtract the original number.
Multiplication by 12: Multiply by 10 and add twice the original number.
Multiplication by 13: Multiply by 3 and add 10 times original number.
Multiplication by 14: Multiply by 7 and then multiply by 2
Multiplication by 15: Multiply by 10 and add 5 times the original number, as above.
Multiplication by 16: You can double four times, if you want to. Or you can multiply by 8 and then by 2.
Multiplication by 17: Multiply by 7 and add 10 times original number.
Multiplication by 18: Multiply by 20 and subtract twice the original number (which is obvious from the first step).
Multiplication by 19: Multiply by 20 and subtract the original number.
Multiplication by 24: Multiply by 8 and then multiply by 3.
Multiplication by 27: Multiply by 30 and subtract 3 times the original number (which is obvious from the first step).
Multiplication by 45: Multiply by 50 and subtract 5 times the original number (which is obvious from the first step).
Multiplication 90: Multiply by 9 (as above) and put a zero on the right.
Multiplication by 98: Multiply by 100 (just place 00 after the original number) and subtract twice the original number.
Multiplication by 99: Multiply by 100 (just place 00 after the original number) and subtract the original number.

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