A trick with numbers ending in 5

Say you want to multiply 4,985 times 7,435 (no calculator)

You can credit this trick to me



Step 1: Drop the 5's (so 498 vs 743)



Step 2: Add 1 to MAX (498, 743) and leave the MIN alone

So we have 498 and 744



Step 3: we need 498 X 744. So happens to be 744/2 * 1000 - (744*2)

A nice 372,000 - 1488 =370,512. Just took 372,000-1500 and added back 12

Again...370,512



Step 4:

Now back to step 1... 498 and 743 (forget about the added 1)

We need 743 minus 498

= 245.

If the number 245 is an odd number, then 4,985*7,435 ends in 75, else it ends in 25

So now we know it ends in 75



Step 5:

Take 245/2 and round it DOWN to the nearest integer ...that's 122



Step 6: 'step 5 result + step 3 result'

122 + 370,512 = 370,634



Step 7: tag on 75 to the step 6

This is the answer

4,985 x 7,435 = 37,063,475



How cool is this? No fancy anything here.

A trick with numbers ending in 5